#------------------------------------------------------------------------------
#
#  Copyright (c) 2007, Enthought, Inc.
#  All rights reserved.
#
#  This software is provided without warranty under the terms of the BSD
#  license included in enthought/LICENSE.txt and may be redistributed only
#  under the conditions described in the aforementioned license.  The license
#  is also available online at http://www.enthought.com/licenses/BSD.txt
#
#  Thanks for using Enthought open source!
#
#  Author: David C. Morrill
#  Date:   03/22/2007
#
#------------------------------------------------------------------------------

""" Core Trait definitions.
"""

#-------------------------------------------------------------------------------
#  Imports:
#-------------------------------------------------------------------------------

from __future__ import absolute_import

import datetime
import operator
import re
import sys
from os.path import isfile, isdir
from types import FunctionType, MethodType, ModuleType

from . import trait_handlers

from .trait_base import (strx, get_module_name, class_of, SequenceTypes, TypeTypes,
        ClassTypes, Undefined, TraitsCache, python_version)

from .trait_handlers import (TraitType, TraitInstance, TraitListObject,
        TraitSetObject, TraitSetEvent, TraitDictObject, TraitDictEvent,
        ThisClass, items_event, RangeTypes, HandleWeakRef)

from .traits import (Trait, trait_from, _TraitMaker, _InstanceArgs, code_editor,
        html_editor, password_editor, shell_editor, date_editor, time_editor)

from .trait_errors import TraitError

from . import _py2to3

#-------------------------------------------------------------------------------
#  Constants:
#-------------------------------------------------------------------------------

MutableTypes = ( list, dict )
SetTypes     = SequenceTypes + ( set, )

#-------------------------------------------------------------------------------
#  Numeric type fast validator definitions:
#-------------------------------------------------------------------------------

# A few words about the next block of code:

# Validator #11 is a generic validator for possibly coercible types
# (see validate_trait_coerce_type in ctraits.c).
#
# The tuples below are of the form
# (11, type1, [type2, type3, ...], [None, ctype1, [ctype2, ...]])
#
# 'type1' corresponds to the main type for the trait
# 'None' acts as the separator between 'types' and 'ctypes' (coercible types)
#
# The validation passes if:
# 1) The trait value type is (a subtype of) one of 'type1', 'type2',  ...
#    in which case the value is returned as-is
# or
# 2) The trait value type is (a subtype of) one of 'ctype1', 'ctype2', ...
#    in which case the value is returned coerced to trait type using
#    'return type1(value')

try:
    # The numpy enhanced definitions:
    from numpy import integer, floating, complexfloating, bool_

    int_fast_validate     = ( 11, int, integer )
    long_fast_validate    = ( 11, long, None, int, integer )
    float_fast_validate   = ( 11, float, floating, None, int, long, integer )
    complex_fast_validate = ( 11, complex, complexfloating, None,
                                  float, floating, int, integer )
    bool_fast_validate    = ( 11, bool, None, bool_ )
    # Tuple or single type suitable for an isinstance check.
    _BOOL_TYPES = (bool, bool_)
except ImportError:
    # The standard python definitions (without numpy):
    int_fast_validate     = ( 11, int )
    long_fast_validate    = ( 11, long,    None, int )
    float_fast_validate   = ( 11, float,   None, int, long )
    complex_fast_validate = ( 11, complex, None, float, int )
    bool_fast_validate    = ( 11, bool )
    # Tuple or single type suitable for an isinstance check.
    _BOOL_TYPES = bool

#-------------------------------------------------------------------------------
#  Returns a default text editor:
#-------------------------------------------------------------------------------

def default_text_editor ( trait, type = None ):
    auto_set = trait.auto_set
    if auto_set is None:
        auto_set = True

    enter_set = trait.enter_set or False

    from traitsui.api import TextEditor

    if type is None:
        return TextEditor( auto_set = auto_set, enter_set = enter_set )

    return TextEditor( auto_set  = auto_set,
                       enter_set = enter_set,
                       evaluate  = type )

#-------------------------------------------------------------------------------
#  'Any' trait:
#-------------------------------------------------------------------------------

class Any ( TraitType ):
    """ Defines a trait whose value can be anything.
    """

    #: The default value for the trait:
    default_value = None

    #: A description of the type of value this trait accepts:
    info_text = 'any value'

#-------------------------------------------------------------------------------
#  'Generic' trait:
#-------------------------------------------------------------------------------

class Generic ( Any ):
    """ Defines a trait whose value can be anything and whose definition can
        be redefined via assignment using a TraitValue object.
    """

    #: The standard metadata for the trait:
    metadata = { 'trait_value': True }

#-------------------------------------------------------------------------------
#  'BaseInt' and 'Int' traits:
#-------------------------------------------------------------------------------

class BaseInt ( TraitType ):
    """ Defines a trait whose type must be an int or long.
    """

    #: The function to use for evaluating strings to this type:
    evaluate = int

    #: The default value for the trait:
    default_value = 0

    #: A description of the type of value this trait accepts:
    info_text = 'an integer (int or long)'

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.
        """
        if type(value) is int:
            return value
        elif type(value) is long:
            return int(value)

        try:
            int_value = operator.index( value )
        except TypeError:
            pass
        else:
            return int(int_value)

        self.error( object, name, value )

    def create_editor ( self ):
        """ Returns the default traits UI editor for this type of trait.
        """
        return default_text_editor( self, int )


class Int ( BaseInt ):
    """ Defines a trait whose type must be an int or long using a C-level fast
        validator.
    """

    #: The C-level fast validator to use:
    fast_validate = ( 20, )

#-------------------------------------------------------------------------------
#  'BaseLong' and 'Long' traits:
#-------------------------------------------------------------------------------

class BaseLong ( TraitType ):
    """ Defines a trait whose value must be a Python long.
    """

    #: The function to use for evaluating strings to this type:
    evaluate = long

    #: The default value for the trait:
    default_value = 0L

    #: A description of the type of value this trait accepts:
    info_text = 'a long'

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        if isinstance( value, long ):
            return value

        if isinstance( value, int ):
            return long( value )

        self.error( object, name, value )

    def create_editor ( self ):
        """ Returns the default traits UI editor for this type of trait.
        """
        return default_text_editor( self, long )


class Long ( BaseLong ):
    """ Defines a trait whose value must be a Python long using a C-level fast
        validator.
    """

    #: The C-level fast validator to use:
    fast_validate = long_fast_validate

#-------------------------------------------------------------------------------
#  'BaseFloat' and 'Float' traits:
#-------------------------------------------------------------------------------

class BaseFloat ( TraitType ):
    """ Defines a trait whose value must be a Python float.
    """
    #: The function to use for evaluating strings to this type:
    evaluate = float

    #: The default value for the trait:
    default_value = 0.0

    #: A description of the type of value this trait accepts:
    info_text = 'a float'

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        if isinstance( value, float ):
            return value

        if isinstance( value, ( int, long ) ):
            return float( value )

        self.error( object, name, value )

    def create_editor ( self ):
        """ Returns the default traits UI editor for this type of trait.
        """
        return default_text_editor( self, float )


class Float ( BaseFloat ):
    """ Defines a trait whose value must be a Python float using a C-level fast
        validator.
    """

    #: The C-level fast validator to use:
    fast_validate = float_fast_validate

#-------------------------------------------------------------------------------
#  'BaseComplex' and 'Complex' traits:
#-------------------------------------------------------------------------------

class BaseComplex ( TraitType ):
    """ Defines a trait whose value must be a Python complex.
    """

    #: The function to use for evaluating strings to this type:
    evaluate = complex

    #: The default value for the trait:
    default_value = 0.0 + 0.0j

    #: A description of the type of value this trait accepts:
    info_text = 'a complex number'

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        if isinstance( value, complex ):
            return value

        if isinstance( value, ( float, int ) ):
            return complex( value )

        self.error( object, name, value )

    def create_editor ( self ):
        """ Returns the default traits UI editor for this type of trait.
        """
        return default_text_editor( self, complex )


class Complex ( BaseComplex ):
    """ Defines a trait whose value must be a Python complex using a C-level
        fast validator.
    """

    #: The C-level fast validator to use:
    fast_validate = complex_fast_validate

#-------------------------------------------------------------------------------
#  'BaseStr' and 'Str' traits:
#-------------------------------------------------------------------------------

class BaseStr ( TraitType ):
    """ Defines a trait whose value must be a Python string.
    """

    #: The default value for the trait:
    default_value = ''

    #: A description of the type of value this trait accepts:
    info_text = 'a string'

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        if isinstance( value, basestring ):
            return value

        self.error( object, name, value )

    def create_editor ( self ):
        """ Returns the default traits UI editor for this type of trait.
        """
        from .traits import multi_line_text_editor
        auto_set = self.auto_set
        if auto_set is None:
            auto_set = True
        enter_set = self.enter_set or False

        return multi_line_text_editor(auto_set, enter_set)


class Str ( BaseStr ):
    """ Defines a trait whose value must be a Python string using a C-level
        fast validator.
    """

    #: The C-level fast validator to use:
    fast_validate = ( 11, basestring )


class Title ( Str ):
    """ Defines a string type which by default uses the traits ui TitleEditor
        when used in a View.
    """

    def create_editor ( self ):
        """ Returns the default traits UI editor to use for a trait.
        """
        from traitsui.api import TitleEditor
        if hasattr(self, 'allow_selection'):
            return TitleEditor(allow_selection=self.allow_selection)
        else:
            return TitleEditor()

#-------------------------------------------------------------------------------
#  'BaseUnicode' and 'Unicode' traits:
#-------------------------------------------------------------------------------

class BaseUnicode ( TraitType ):
    """ Defines a trait whose value must be a Python unicode string.
    """

    #: The default value for the trait:
    default_value = u''

    #: A description of the type of value this trait accepts:
    info_text = 'a unicode string'

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        if isinstance( value, unicode ):
            return value

        if isinstance( value, str ):
            return unicode( value )

        self.error( object, name, value )

    def create_editor ( self ):
        """ Returns the default traits UI editor for this type of trait.
        """
        from .traits import multi_line_text_editor
        auto_set = self.auto_set
        if auto_set is None:
            auto_set = True
        enter_set = self.enter_set or False

        return multi_line_text_editor(auto_set, enter_set)


class Unicode ( BaseUnicode ):
    """ Defines a trait whose value must be a Python unicode string using a
        C-level fast validator.
    """

    #: The C-level fast validator to use:
    fast_validate = ( 11, unicode, None, str )


#-------------------------------------------------------------------------------
#  'BaseBytes' and 'Bytes' traits:
#-------------------------------------------------------------------------------

class BaseBytes(TraitType):
    """ Defines a trait whose value must be a Python bytes string.
    """

    #: The default value for the trait:
    default_value = b''

    #: A description of the type of value this trait accepts:
    info_text = 'a bytes string'

    #: An encoding to use with TraitsUI editors
    encoding = None

    def validate(self, object, name, value):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        if isinstance(value, bytes):
            return value

        self.error(object, name, value)

    def create_editor(self):
        """ Returns the default traits UI editor for this type of trait.
        """
        from .traits import bytes_editor
        auto_set = self.auto_set
        if auto_set is None:
            auto_set = True
        enter_set = self.enter_set or False

        return bytes_editor(auto_set, enter_set, self.encoding)


class Bytes(BaseBytes):
    """ Defines a trait whose value must be a Python bytes string using a
        C-level fast validator.
    """

    #: The C-level fast validator to use:
    fast_validate = (11, bytes)

#-------------------------------------------------------------------------------
#  'BaseBool' and 'Bool' traits:
#-------------------------------------------------------------------------------

class BaseBool ( TraitType ):
    """ Defines a trait whose value must be a Python boolean.
    """

    #: The function to use for evaluating strings to this type:
    evaluate = bool

    #: The default value for the trait:
    default_value = False

    #: A description of the type of value this trait accepts:
    info_text = 'a boolean'

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        if isinstance( value, _BOOL_TYPES ):
            return bool(value)

        self.error( object, name, value )

    def create_editor ( self ):
        """ Returns the default traits UI editor for this type of trait.
        """
        from traitsui.api import BooleanEditor

        return BooleanEditor()


class Bool ( BaseBool ):
    """ Defines a trait whose value must be a Python boolean using a C-level
        fast validator.
    """

    #: The C-level fast validator to use:
    fast_validate = bool_fast_validate

#-------------------------------------------------------------------------------
#  'BaseCInt' and 'CInt' traits:
#-------------------------------------------------------------------------------

class BaseCInt ( BaseInt ):
    """ Defines a trait whose value must be a Python int and which supports
        coercions of non-int values to int.
    """

    #: The function to use for evaluating strings to this type:
    evaluate = int

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        try:
            return int( value )
        except:
            self.error( object, name, value )


class CInt ( BaseCInt ):
    """ Defines a trait whose value must be a Python int and which supports
        coercions of non-int values to int using a C-level fast validator.
    """

    #: The C-level fast validator to use:
    fast_validate = ( 12, int )

#-------------------------------------------------------------------------------
#  'BaseCLong' and 'CLong' traits:
#-------------------------------------------------------------------------------

class BaseCLong ( BaseLong ):
    """ Defines a trait whose value must be a Python long and which supports
        coercions of non-long values to long.
    """

    #: The function to use for evaluating strings to this type:
    evaluate = long

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        try:
            return long( value )
        except:
            self.error( object, name, value )


class CLong ( BaseCLong ):
    """ Defines a trait whose value must be a Python long and which supports
        coercions of non-long values to long using a C-level fast validator.
    """

    #: The C-level fast validator to use:
    fast_validate = ( 12, long )

#-------------------------------------------------------------------------------
#  'BaseCFloat' and 'CFloat' traits:
#-------------------------------------------------------------------------------

class BaseCFloat ( BaseFloat ):
    """ Defines a trait whose value must be a Python float and which supports
        coercions of non-float values to float.
    """

    #: The function to use for evaluating strings to this type:
    evaluate = float

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        try:
            return float( value )
        except:
            self.error( object, name, value )


class CFloat ( BaseCFloat ):
    """ Defines a trait whose value must be a Python float and which supports
        coercions of non-float values to float using a C-level fast validator.
    """

    #: The C-level fast validator to use:
    fast_validate = ( 12, float )

#-------------------------------------------------------------------------------
#  'BaseCComplex' and 'CComplex' traits:
#-------------------------------------------------------------------------------

class BaseCComplex ( BaseComplex ):
    """ Defines a trait whose value must be a Python complex and which supports
        coercions of non-complex values to complex.
    """

    #: The function to use for evaluating strings to this type:
    evaluate = complex

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        try:
            return complex( value )
        except:
            self.error( object, name, value )


class CComplex ( BaseCComplex ):
    """ Defines a trait whose value must be a Python complex and which supports
        coercions of non-complex values to complex using a C-level fast
        validator.
    """

    #: The C-level fast validator to use:
    fast_validate = ( 12, complex )

#-------------------------------------------------------------------------------
#  'BaseCStr' and 'CStr' traits:
#-------------------------------------------------------------------------------

class BaseCStr ( BaseStr ):
    """ Defines a trait whose value must be a Python string and which supports
        coercions of non-string values to string.
    """

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        try:
            return str( value )
        except:
            try:
                return unicode( value )
            except:
                self.error( object, name, value )


class CStr ( BaseCStr ):
    """ Defines a trait whose value must be a Python string and which supports
        coercions of non-string values to string using a C-level fast
        validator.
    """

    #: The C-level fast validator to use:
    fast_validate = ( 7, ( ( 12, str ), ( 12, unicode ) ) )

#-------------------------------------------------------------------------------
#  'BaseCUnicode' and 'CUnicode' traits:
#-------------------------------------------------------------------------------

class BaseCUnicode ( BaseUnicode ):
    """ Defines a trait whose value must be a Python unicode string and which
        supports coercions of non-unicode values to unicode.
    """

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        try:
            return unicode( value )
        except:
            self.error( object, name, value )


class CUnicode ( BaseCUnicode ):
    """ Defines a trait whose value must be a Python unicode string and which
        supports coercions of non-unicode values to unicode using a C-level
        fast validator.
    """

    #: The C-level fast validator to use:
    fast_validate = ( 12, unicode )

#-------------------------------------------------------------------------------
#  'BaseCBytes' and 'CBytes' traits:
#-------------------------------------------------------------------------------

class BaseCBytes(BaseBytes):
    """ Defines a trait whose value must be a Python bytes object and which
        supports coercions of non-bytes values to bytes.
    """

    def validate(self, object, name, value):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        try:
            return bytes(value)
        except:
            self.error(object, name, value)


class CBytes(BaseCBytes):
    """ Defines a trait whose value must be a Python bytes and which
        supports coercions of non-bytes values bytes using a C-level
        fast validator.
    """

    #: The C-level fast validator to use:
    fast_validate = (12, bytes)

#-------------------------------------------------------------------------------
#  'BaseCBool' and 'CBool' traits:
#-------------------------------------------------------------------------------

class BaseCBool ( BaseBool ):
    """ Defines a trait whose value must be a Python boolean and which supports
        coercions of non-boolean values to boolean.
    """

    #: The function to use for evaluating strings to this type:
    evaluate = bool

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        try:
            return bool( value )
        except:
            self.error( object, name, value )


class CBool ( BaseCBool ):
    """ Defines a trait whose value must be a Python boolean and which supports
        coercions of non-boolean values to boolean using a C-level fast
        validator.
    """

    #: The C-level fast validator to use:
    fast_validate = ( 12, bool )

#-------------------------------------------------------------------------------
#  'String' trait:
#-------------------------------------------------------------------------------

class String ( TraitType ):
    """ Defines a trait whose value must be a Python string whose length is
        optionally in a specified range, and which optionally matches a
        specified regular expression.
    """

    def __init__ ( self, value = '', minlen = 0, maxlen = sys.maxint,
                   regex = '', **metadata ):
        """ Creates a String trait.

        Parameters
        ----------
        value : str
            The default value for the string.
        minlen : integer
            The minimum length allowed for the string.
        maxlen : integer
            The maximum length allowed for the string.
        regex : str
            A Python regular expression that the string must match.

        """
        super( String, self ).__init__( value, **metadata )
        self.minlen = max( 0, minlen )
        self.maxlen = max( self.minlen, maxlen )
        self.regex  = regex
        self._init()

    def _init ( self ):
        """ Completes initialization of the trait at construction or unpickling
            time.
        """
        self._validate = 'validate_all'
        if self.regex != '':
            self.match = re.compile( self.regex ).match
            if (self.minlen == 0) and (self.maxlen == sys.maxint):
                self._validate = 'validate_regex'
        elif (self.minlen == 0) and (self.maxlen == sys.maxint):
            self._validate = 'validate_str'
        else:
            self._validate = 'validate_len'

    def validate ( self, object, name, value ):
        """ Validates that the value is a valid string.
        """
        return getattr( self, self._validate )( object, name, value )

    def validate_all ( self, object, name, value ):
        """ Validates that the value is a valid string in the specified length
            range which matches the specified regular expression.
        """
        try:
            value = strx( value )
            if ((self.minlen <= len( value ) <= self.maxlen) and
                (self.match( value ) is not None)):
                return value
        except:
            pass

        self.error( object, name, value )

    def validate_str ( self, object, name, value ):
        """ Validates that the value is a valid string.
        """
        try:
            return strx( value )
        except:
            pass

        self.error( object, name, value )

    def validate_len ( self, object, name, value ):
        """ Validates that the value is a valid string in the specified length
            range.
        """
        try:
            value = strx( value )
            if self.minlen <= len( value ) <= self.maxlen:
                return value
        except:
            pass

        self.error( object, name, value )

    def validate_regex ( self, object, name, value ):
        """ Validates that the value is a valid string which matches the
            specified regular expression.
        """
        try:
            value = strx( value )
            if self.match( value ) is not None:
                return value
        except:
            pass

        self.error( object, name, value )

    def info ( self ):
        """ Returns a description of the trait.
        """
        msg = ''
        if (self.minlen != 0) and (self.maxlen != sys.maxint):
            msg = ' between %d and %d characters long' % (
                  self.minlen, self.maxlen )
        elif self.maxlen != sys.maxint:
            msg = ' <= %d characters long' % self.maxlen
        elif self.minlen != 0:
            msg = ' >= %d characters long' % self.minlen
        if self.regex != '':
            if msg != '':
                msg += ' and'
            msg += (" matching the pattern '%s'" % self.regex)
        return 'a string' + msg

    def create_editor ( self ):
        """ Returns the default traits UI editor for this type of trait.
        """
        return default_text_editor( self )

    def __getstate__ ( self ):
        """ Returns the current state of the trait.
        """
        result = self.__dict__.copy()
        for name in [ 'validate', 'match' ]:
            if name in result:
                del result[ name ]

        return result

    def __setstate__ ( self, state ):
        """ Sets the current state of the trait.
        """
        self.__dict__.update( state )
        self._init()

#-------------------------------------------------------------------------------
#  'Regex' trait:
#-------------------------------------------------------------------------------

class Regex ( String ):
    """ Defines a trait whose value is a Python string that matches a specified
        regular expression.
    """

    def __init__ ( self, value = '', regex = '.*', **metadata ):
        """ Creates a Regex trait.

        Parameters
        ----------
        value : str
            The default value of the trait.
        regex : str
            The regular expression that the trait value must match.

        Default Value
        -------------
        *value* or ''
        """
        super( Regex, self ).__init__( value = value, regex = regex,
                                       **metadata )

#-------------------------------------------------------------------------------
#  'Code' trait:
#-------------------------------------------------------------------------------

class Code ( String ):
    """ Defines a trait whose value is a Python string that represents source
        code in some language.
    """

    #: The standard metadata for the trait:
    metadata = { 'editor': code_editor }

#-------------------------------------------------------------------------------
#  'HTML' trait:
#-------------------------------------------------------------------------------

class HTML ( String ):
    """ Defines a trait whose value must be a string that is interpreted as
    being HTML. By default the value is parsed and displayed as HTML in
    TraitsUI views. The validation of the value does not enforce HTML syntax.
    """

    #: The standard metadata for the trait:
    metadata = { 'editor': html_editor }

#-------------------------------------------------------------------------------
#  'Password' trait:
#-------------------------------------------------------------------------------

class Password ( String ):
    """ Defines a trait whose value must be a string, optionally of constrained
    length or matching a regular expression.

    The trait is identical to a String trait except that by default it uses a
    PasswordEditor in TraitsUI views, which obscures text entered by the user.
    """

    #: The standard metadata for the trait:
    metadata = { 'editor': password_editor }

#-------------------------------------------------------------------------------
#  'Callable' trait:
#-------------------------------------------------------------------------------

class Callable ( TraitType ):
    """ Defines a trait whose value must be a Python callable.
    """

    #: The standard metadata for the trait:
    metadata = { 'copy': 'ref' }

    #: The default value for the trait:
    default_value = None

    #: A description of the type of value this trait accepts:
    info_text = 'a callable value'

    def validate ( self, object, name, value ):
        """ Validates that the value is a Python callable.
        """
        if (value is None) or callable( value ):
            return value

        self.error( object, name, value )

#-------------------------------------------------------------------------------
#  'BaseType' base class:
#-------------------------------------------------------------------------------

class BaseType ( TraitType ):
    """ Defines a trait whose value must be an instance of a simple Python type.
    """

    def validate ( self, object, name, value ):
        """ Validates that the value is a Python callable.
        """
        if isinstance( value, self.fast_validate[1:] ):
            return value

        self.error( object, name, value )


class This ( BaseType ):
    """ Defines a trait whose value must be an instance of the defining class.
    """

    #: The C-level fast validator to use:
    fast_validate = ( 2, )

    #: A description of the type of value this trait accepts:
    info_text = 'an instance of the same type as the receiver'

    def __init__ ( self, value = None, allow_none = True, **metadata ):
        super( This, self ).__init__( value, **metadata )

        if allow_none:
            self.fast_validate = ( 2, None )
            self.validate      = self.validate_none
            self.info          = self.info_none

    def validate ( self, object, name, value ):
        if isinstance( value, object.__class__ ):
            return value

        self.validate_failed( object, name, value )

    def validate_none ( self, object, name, value ):
        if isinstance( value, object.__class__ ) or (value is None):
            return value

        self.validate_failed( object, name, value )

    def info ( self ):
        return 'an instance of the same type as the receiver'

    def info_none ( self ):
        return 'an instance of the same type as the receiver or None'

    def validate_failed ( self, object, name, value ):
        kind = type( value )
        if _py2to3.is_InstanceType(kind):
            msg = 'class %s' % value.__class__.__name__
        else:
            msg = '%s (i.e. %s)' % ( str( kind )[1:-1], repr( value ) )

        self.error( object, name, msg )


class self ( This ):
    """ Defines a trait whose value must be an instance of the defining class
        and whose default value is the object containing the trait.
    """

    #: The default value type to use (i.e. 'self'):
    default_value_type = 2


class Function ( TraitType ):
    """ Defines a trait whose value must be a Python function.
    """

    #: The C-level fast validator to use:
    fast_validate = ( 11, FunctionType )

    #: A description of the type of value this trait accepts:
    info_text = 'a function'


class Method ( TraitType ):
    """ Defines a trait whose value must be a Python method.
    """

    #: The C-level fast validator to use:
    fast_validate = ( 11, MethodType )

    #: A description of the type of value this trait accepts:
    info_text = 'a method'

if sys.version_info[0] < 3:
    from types import ClassType

    class Class ( TraitType ):
        """ Defines a trait whose value must be an old-style Python class.
        """

        #: The C-level fast validator to use:
        fast_validate = ( 11, ClassType )

        #: A description of the type of value this trait accepts:
        info_text = 'an old-style class'


class Module ( TraitType ):
    """ Defines a trait whose value must be a Python module.
    """

    #: The C-level fast validator to use:
    fast_validate = ( 11, ModuleType )

    #: A description of the type of value this trait accepts:
    info_text = 'a module'

#-------------------------------------------------------------------------------
#  'Python' trait:
#-------------------------------------------------------------------------------

class Python ( TraitType ):
    """ Defines a trait that provides behavior identical to a standard Python
        attribute. That is, it allows any value to be assigned, and raises an
        ValueError if an attempt is made to get the value before one has been
        assigned. It has no default value. This trait is most often used in
        conjunction with wildcard naming. See the *Traits User Manual* for
        details on wildcards.
    """

    #: The standard metadata for the trait:
    metadata = { 'type': 'python' }

    #: The default value for the trait:
    default_value = Undefined

#-------------------------------------------------------------------------------
#  'ReadOnly' trait:
#-------------------------------------------------------------------------------

class ReadOnly ( TraitType ):
    """ Defines a trait that is write-once, and then read-only.
        The initial value of the attribute is the special, singleton object
        Undefined. The trait allows any value to be assigned to the attribute
        if the current value is the Undefined object. Once any other value is
        assigned, no further assignment is allowed. Normally, the initial
        assignment to the attribute is performed in the class constructor,
        based on information passed to the constructor. If the read-only value
        is known in advance of run time, use the Constant() function instead of
        ReadOnly to define the trait.
    """

    # Defines the CTrait type to use for this trait:
    ctrait_type = 6

    #: The default value for the trait:
    default_value = Undefined

# Create a singleton instance as the trait:
ReadOnly = ReadOnly()

#-------------------------------------------------------------------------------
#  'Disallow' trait:
#-------------------------------------------------------------------------------

class Disallow ( TraitType ):
    """ Defines a trait that prevents any value from being assigned or read.
        That is, any attempt to get or set the value of the trait attribute
        raises an exception. This trait is most often used in conjunction with
        wildcard naming, for example, to catch spelling mistakes in attribute
        names. See the *Traits User Manual* for details on wildcards.
    """

    #: Defines the CTrait type to use for this trait:
    ctrait_type = 5

# Create a singleton instance as the trait:
Disallow = Disallow()

#-------------------------------------------------------------------------------
#  'Constant' trait:
#-------------------------------------------------------------------------------

class Constant ( TraitType ):
    """  Defines a trait whose value is a constant.
    """

    #: Defines the CTrait type to use for this trait:
    ctrait_type = 7

    #: The standard metadata for the trait:
    metadata = { 'type': 'constant', 'transient': True }

    def __init__ ( self, value, **metadata ):
        """ Returns a constant, read-only trait whose value is *value*.

            Parameters
            ----------
            value : any type except a list or dictionary
                The default value for the trait.

            Default Value
            -------------
            *value*

            Description
            -----------
            Traits of this type are very space efficient (and fast) because
            *value* is not stored in each instance using the trait, but only in
            the trait object itself. The *value* cannot be a list or dictionary,
            because those types have mutable values.
        """
        if type( value ) in MutableTypes:
            raise TraitError, \
                  "Cannot define a constant using a mutable list or dictionary"

        super( Constant, self ).__init__( value, **metadata )

#-------------------------------------------------------------------------------
#  'Delegate' trait:
#-------------------------------------------------------------------------------

class Delegate ( TraitType ):
    """ Defines a trait whose value is delegated to a trait on another object.
    """

    #: Defines the CTrait type to use for this trait:
    ctrait_type = 3

    #: The standard metadata for the trait:
    metadata = { 'type': 'delegate', 'transient': False }

    def __init__ ( self, delegate, prefix = '', modify = False,
                         listenable = True, **metadata ):
        """ Creates a Delegate trait.
        """
        if prefix == '':
            prefix_type = 0
        elif prefix[-1:] != '*':
            prefix_type = 1
        else:
            prefix = prefix[:-1]
            if prefix != '':
                prefix_type = 2
            else:
                prefix_type = 3

        metadata[ '_delegate' ]   = delegate
        metadata[ '_prefix' ]     = prefix
        metadata[ '_listenable' ] = listenable

        super( Delegate, self ).__init__( **metadata )

        self.delegate    = delegate
        self.prefix      = prefix
        self.prefix_type = prefix_type
        self.modify      = modify

    def as_ctrait ( self ):
        """ Returns a CTrait corresponding to the trait defined by this class.
        """
        trait = super( Delegate, self ).as_ctrait()
        trait.delegate( self.delegate, self.prefix, self.prefix_type,
                        self.modify )

        return trait

#-------------------------------------------------------------------------------
#  'DelegatesTo' trait:
#-------------------------------------------------------------------------------

class DelegatesTo ( Delegate ):
    """ Defines a trait delegate that matches the standard 'delegate' design
        pattern.
    """

    def __init__ ( self, delegate, prefix = '', listenable = True, **metadata ):
        """ Creates a "delegator" trait, whose definition and default value are
            delegated to a *delegate* trait attribute on another object.

            Parameters
            ----------
            delegate : str
                Name of the attribute on the current object which references
                the object that is the trait's delegate.
            prefix : str
                A prefix or substitution applied to the original attribute when
                looking up the delegated attribute.
            listenable : bool
                Indicates whether a listener can be attached to this attribute
                such that changes to the delagate attribute will trigger it.

            Description
            -----------
            An object containing a delegator trait attribute must contain a
            second attribute that references the object containing the delegate
            trait attribute. The name of this second attribute is passed as the
            *delegate* argument to the DelegatesTo() function.

            The following rules govern the application of the prefix parameter:

            * If *prefix* is empty or omitted, the delegation is to an attribute
              of the delegate object with the same name as the delegator
              attribute.
            * If *prefix* is a valid Python attribute name, then the delegation
              is to an attribute whose name is the value of *prefix*.
            * If *prefix* ends with an asterisk ('*') and is longer than one
              character, then the delegation is to an attribute whose name is
              the value of *prefix*, minus the trailing asterisk, prepended to
              the delegator attribute name.
            * If *prefix* is equal to a single asterisk, the delegation is to an
              attribute whose name is the value of the delegator object's
              __prefix__ attribute prepended to delegator attribute name.

            Note that any changes to the delegator attribute are actually
            applied to the corresponding attribute on the delegate object. The
            original object containing the delegator trait is not modified.
        """
        super( DelegatesTo, self ).__init__( delegate,
                                             prefix     = prefix,
                                             modify     = True,
                                             listenable = listenable,
                                             **metadata )

#-------------------------------------------------------------------------------
#  'PrototypedFrom' trait:
#-------------------------------------------------------------------------------

class PrototypedFrom ( Delegate ):
    """ Defines a trait delegate that matches the standard 'prototype' design
        pattern.
    """

    def __init__ ( self, prototype, prefix = '', listenable = True,
                         **metadata ):
        """ Creates a "prototyped" trait, whose definition and default value are
            obtained from a trait attribute on another object.

            Parameters
            ----------
            prototype : str
                Name of the attribute on the current object which references the
                object that is the trait's prototype.
            prefix : str
                A prefix or substitution applied to the original attribute when
                looking up the prototyped attribute.
            listenable : bool
                Indicates whether a listener can be attached to this attribute
                such that changes to the corresponding attribute on the
                prototype object will trigger it.

            Description
            -----------
            An object containing a prototyped trait attribute must contain a
            second attribute that references the object containing the prototype
            trait attribute. The name of this second attribute is passed as the
            *prototype* argument to the PrototypedFrom() function.

            The following rules govern the application of the prefix parameter:

            * If *prefix* is empty or omitted, the prototype delegation is to an
              attribute of the prototype object with the same name as the
              prototyped attribute.
            * If *prefix* is a valid Python attribute name, then the prototype
              delegation is to an attribute whose name is the value of *prefix*.
            * If *prefix* ends with an asterisk ('*') and is longer than one
              character, then the prototype delegation is to an attribute whose
              name is the value of *prefix*, minus the trailing asterisk,
              prepended to the prototyped attribute name.
            * If *prefix* is equal to a single asterisk, the prototype
              delegation is to an attribute whose name is the value of the
              prototype object's __prefix__ attribute prepended to the
              prototyped attribute name.

            Note that any changes to the prototyped attribute are made to the
            original object, not the prototype object. The prototype object is
            only used to define to trait type and default value.

        """
        super( PrototypedFrom, self ).__init__( prototype,
                                                prefix     = prefix,
                                                modify     = False,
                                                listenable = listenable,
                                                **metadata )

#-------------------------------------------------------------------------------
#  'Expression' class:
#-------------------------------------------------------------------------------

class Expression ( TraitType ):
    """ Defines a trait whose value must be a valid Python expression. The
        compiled form of a valid expression is stored as the mapped value of
        the trait.
    """

    #: The default value for the trait:
    default_value = '0'

    #: A description of the type of value this trait accepts:
    info_text = 'a valid Python expression'

    #: Indicate that this is a mapped trait:
    is_mapped = True

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.
        """
        try:
            return compile( value, '<string>', 'eval' )
        except:
            self.error( object, name, value )

    def post_setattr ( self, object, name, value ):
        """ Performs additional post-assignment processing.
        """
        object.__dict__[ name + '_' ] = value

    def mapped_value ( self, value ):
        """ Returns the 'mapped' value for the specified **value**.
        """
        return compile( value, '<string>', 'eval' )

    def as_ctrait ( self ):
        """ Returns a CTrait corresponding to the trait defined by this class.
        """
        # Tell the C code that 'setattr' should store the original, unadapted
        # value passed to it:
        return super( Expression, self
                    ).as_ctrait().setattr_original_value( True )

#-------------------------------------------------------------------------------
#  'PythonValue' trait:
#-------------------------------------------------------------------------------

class PythonValue ( Any ):
    """ Defines a trait whose value can be of any type, and whose default
    editor is a Python shell.
    """

    #: The standard metadata for the trait:
    metadata = { 'editor': shell_editor }

#-------------------------------------------------------------------------------
#  'BaseFile' and 'File' traits:
#-------------------------------------------------------------------------------

class BaseFile ( BaseStr ):
    """ Defines a trait whose value must be the name of a file.
    """

    #: A description of the type of value this trait accepts:
    info_text = 'a file name'

    def __init__ ( self, value = '', filter = None, auto_set = False,
                         entries = 0, exists = False, **metadata ):
        """ Creates a File trait.

        Parameters
        ----------
        value : str
            The default value for the trait.
        filter : str
            A wildcard string to filter filenames in the file dialog box used by
            the attribute trait editor.
        auto_set : bool
            Indicates whether the file editor updates the trait value after
            every key stroke.
        exists : bool
            Indicates whether the trait value must be an existing file or
            not.

        Default Value
        -------------
        *value* or ''
        """
        self.filter = filter
        self.auto_set = auto_set
        self.entries = entries
        self.exists = exists

        super( BaseFile, self ).__init__( value, **metadata )

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        validated_value = super( BaseFile, self ).validate( object, name, value )
        if not self.exists:
            return validated_value
        elif isfile( value ):
            return validated_value

        self.error( object, name, value )

    def create_editor(self):
        from traitsui.editors.file_editor import FileEditor
        editor = FileEditor(
            filter = self.filter or [],
            auto_set = self.auto_set,
            entries = self.entries,
        )
        return editor


class File ( BaseFile ):
    """ Defines a trait whose value must be the name of a file using a C-level
        fast validator.
    """

    def __init__ ( self, value = '', filter = None, auto_set = False,
                         entries = 0, exists = False, **metadata ):
        """ Creates a File trait.

        Parameters
        ----------
        value : str
            The default value for the trait.
        filter : str
            A wildcard string to filter filenames in the file dialog box used
            by the attribute trait editor.
        auto_set : bool
            Indicates whether the file editor updates the trait value after
            every key stroke.
        exists : bool
            Indicates whether the trait value must be an existing file or
            not.

        Default Value
        -------------
        *value* or ''
        """
        if not exists:
            # Define the C-level fast validator to use:
            fast_validate = ( 11, basestring )

        super( File, self ).__init__( value, filter, auto_set, entries, exists,
                                      **metadata )

#-------------------------------------------------------------------------------
#  'BaseDirectory' and 'Directory' traits:
#-------------------------------------------------------------------------------

class BaseDirectory ( BaseStr ):
    """ Defines a trait whose value must be the name of a directory.
    """

    #: A description of the type of value this trait accepts:
    info_text = 'a directory name'

    def __init__ ( self, value = '', auto_set = False, entries = 0,
                         exists = False, **metadata ):
        """ Creates a BaseDirectory trait.

        Parameters
        ----------
        value : str
            The default value for the trait.
        auto_set : bool
            Indicates whether the directory editor updates the trait value
            after every key stroke.
        exists : bool
            Indicates whether the trait value must be an existing directory or
            not.

        Default Value
        -------------
        *value* or ''
        """
        self.entries = entries
        self.auto_set = auto_set
        self.exists = exists

        super( BaseDirectory, self ).__init__( value, **metadata )

    def validate ( self, object, name, value ):
        """ Validates that a specified value is valid for this trait.

            Note: The 'fast validator' version performs this check in C.
        """
        if not self.exists:
            return super( BaseDirectory, self ).validate( object, name, value )

        if isdir( value ):
            return value

        self.error( object, name, value )

    def create_editor(self):
        from traitsui.editors.directory_editor import DirectoryEditor
        editor = DirectoryEditor(
            auto_set = self.auto_set,
            entries = self.entries,
        )
        return editor


class Directory ( BaseDirectory ):
    """ Defines a trait whose value must be the name of a directory using a
        C-level fast validator.
    """

    def __init__ ( self, value = '', auto_set = False, entries = 0,
                         exists = False, **metadata ):
        """ Creates a Directory trait.

        Parameters
        ----------
        value : str
            The default value for the trait.
        auto_set : bool
            Indicates whether the directory editor updates the trait value
            after every key stroke.
        exists : bool
            Indicates whether the trait value must be an existing directory or
            not.

        Default Value
        -------------
        *value* or ''
        """
        # Define the C-level fast validator to use if the directory existence
        #: test is not required:
        if not exists:
            self.fast_validate = ( 11, basestring )

        super( Directory, self ).__init__( value, auto_set, entries, exists,
                                           **metadata )

#-------------------------------------------------------------------------------
#  'BaseRange' and 'Range' traits:
#-------------------------------------------------------------------------------

class BaseRange ( TraitType ):
    """ Defines a trait whose numeric value must be in a specified range.
    """

    def __init__ ( self, low = None, high = None, value = None,
                         exclude_low = False, exclude_high = False,
                         **metadata ):
        """ Creates a Range trait.

        Parameters
        ----------
        low : integer, float or string (i.e. extended trait name)
            The low end of the range.
        high : integer, float or string (i.e. extended trait name)
            The high end of the range.
        value : integer, float or string (i.e. extended trait name)
            The default value of the trait.
        exclude_low : bool
            Indicates whether the low end of the range is exclusive.
        exclude_high : bool
            Indicates whether the high end of the range is exclusive.

        The *low*, *high*, and *value* arguments must be of the same type
        (integer or float), except in the case where either *low* or *high* is
        a string (i.e. extended trait name).

        Default Value
        -------------
        *value*; if *value* is None or omitted, the default value is *low*,
        unless *low* is None or omitted, in which case the default value is
        *high*.
        """
        if value is None:
            if low is not None:
                value = low
            else:
                value = high

        super( BaseRange, self ).__init__( value, **metadata )

        vtype = type( high )
        if ((low is not None) and
            (not issubclass( vtype, ( float, basestring ) ))):
            vtype = type( low )

        is_static = (not issubclass( vtype, basestring ))
        if is_static and (vtype not in RangeTypes):
            raise TraitError, ("Range can only be use for int, long or float "
                               "values, but a value of type %s was specified." %
                               vtype)

        self._low_name = self._high_name = ''
        self._vtype    = Undefined

        if vtype is float:
            self._validate  = 'float_validate'
            kind            = 4
            self._type_desc = 'a floating point number'
            if low is not None:
                low = float( low )

            if high is not None:
                high = float( high )

        elif vtype is long:
            self._validate  = 'long_validate'
            self._type_desc = 'a long integer'
            if low is not None:
                low = long( low )

            if high is not None:
                high = long( high )

        elif vtype is int:
            self._validate  = 'int_validate'
            kind            = 3
            self._type_desc = 'an integer'
            if low is not None:
                low = int( low )

            if high is not None:
                high = int( high )
        else:
            self.get, self.set, self.validate = self._get, self._set, None
            self._vtype     = None
            self._type_desc = 'a number'

            if isinstance( high, basestring ):
                self._high_name = high = 'object.' + high
            else:
                self._vtype = type( high )
            high = compile( str( high ), '<string>', 'eval' )

            if isinstance( low, basestring ):
                self._low_name = low = 'object.' + low
            else:
                self._vtype = type( low )
            low = compile( str( low ), '<string>', 'eval' )

            if isinstance( value, basestring ):
                value = 'object.' + value
            self._value = compile( str( value ), '<string>', 'eval' )

            self.default_value_type = 8
            self.default_value      = self._get_default_value

        exclude_mask = 0
        if exclude_low:
            exclude_mask |= 1

        if exclude_high:
            exclude_mask |= 2

        if is_static and (vtype is not long):
            self.init_fast_validator( kind, low, high, exclude_mask )

        #: Assign type-corrected arguments to handler attributes:
        self._low          = low
        self._high         = high
        self._exclude_low  = exclude_low
        self._exclude_high = exclude_high

    def init_fast_validator ( self, *args ):
        """ Does nothing for the BaseRange class. Used in the Range class to
            set up the fast validator.
        """
        pass

    def validate ( self, object, name, value ):
        """ Validate that the value is in the specified range.
        """
        return getattr( self, self._validate )( object, name, value )

    def float_validate ( self, object, name, value ):
        """ Validate that the value is a float value in the specified range.
        """
        try:
            if (isinstance( value, RangeTypes ) and
                ((self._low is None) or
                 (self._exclude_low and (self._low < value)) or
                 ((not self._exclude_low) and (self._low <= value))) and
                ((self._high is None) or
                 (self._exclude_high and (self._high > value)) or
                 ((not self._exclude_high) and (self._high >= value)))):
               return float( value )
        except:
            pass

        self.error( object, name, value )

    def int_validate ( self, object, name, value ):
        """ Validate that the value is an int value in the specified range.
        """
        try:
            if (isinstance( value, int_fast_validate[1:]) and
                ((self._low is None) or
                 (self._exclude_low and (self._low < value)) or
                 ((not self._exclude_low) and (self._low <= value))) and
                ((self._high is None) or
                 (self._exclude_high and (self._high > value)) or
                 ((not self._exclude_high) and (self._high >= value)))):
               return value
        except:
            pass

        self.error( object, name, value )

    def long_validate ( self, object, name, value ):
        """ Validate that the value is a long value in the specified range.
        """
        try:
            valid_types = list(long_fast_validate[1:])
            valid_types.remove(None)
            if (isinstance( value, tuple(valid_types) ) and
                ((self._low is None) or
                 (self._exclude_low and (self._low < value)) or
                 ((not self._exclude_low) and (self._low <= value))) and
                ((self._high is None) or
                 (self._exclude_high and (self._high > value)) or
                 ((not self._exclude_high) and (self._high >= value)))):
               return value
        except:
            pass

        self.error( object, name, value )

    def _get_default_value ( self, object ):
        """ Returns the default value of the range.
        """
        return eval( self._value )

    def _get ( self, object, name, trait ):
        """ Returns the current value of a dynamic range trait.
        """
        cname = '_traits_cache_' + name
        value = object.__dict__.get( cname, Undefined )
        if value is Undefined:
            object.__dict__[ cname ] = value = eval( self._value )

        low  = eval( self._low )
        high = eval( self._high )
        if (low is not None) and (value < low):
            value = low
        elif (high is not None) and (value > high):
            value = high

        return self._typed_value( value, low, high )

    def _set ( self, object, name, value ):
        """ Sets the current value of a dynamic range trait.
        """
        if not isinstance( value, basestring ):
            try:
                low  = eval( self._low )
                high = eval( self._high )
                if (low is None) and (high is None):
                    if isinstance( value, RangeTypes ):
                        self._set_value( object, name, value )
                        return
                else:
                    new_value = self._typed_value( value, low, high )
                    if (((low is None) or
                        (self._exclude_low and (low < new_value)) or
                        ((not self._exclude_low) and (low <= new_value))) and
                        ((high is None) or
                        (self._exclude_high and (high > new_value)) or
                        ((not self._exclude_high) and (high >= new_value)))):
                        self._set_value( object, name, new_value )
                        return
            except:
                pass

        self.error( object, name, value )

    def _typed_value ( self, value, low, high ):
        """ Returns the specified value with the correct type for the current
            dynamic range.
        """
        vtype = self._vtype
        if vtype is None:
            if low is not None:
                vtype = type( low )
            elif high is not None:
                vtype = type( high )
            else:
                vtype = lambda x: x

        return vtype( value )

    def _set_value ( self, object, name, value ):
        """ Sets the specified value as the value of the dynamic range.
        """
        cname = '_traits_cache_' + name
        old   = object.__dict__.get( cname, Undefined )
        if old is Undefined:
            old = eval( self._value )
        object.__dict__[ cname ] = value
        if value != old:
            object.trait_property_changed( name, old, value )

    def full_info ( self, object, name, value ):
        """ Returns a description of the trait.
        """
        if self._vtype is not Undefined:
            low       = eval( self._low )
            high      = eval( self._high )
            low, high = ( self._typed_value( low,  low, high ),
                          self._typed_value( high, low, high ) )
        else:
            low  = self._low
            high = self._high

        if low is None:
            if high is None:
                return self._type_desc

            return '%s <%s %s' % (
                   self._type_desc, '='[ self._exclude_high: ], high )

        elif high is None:
            return  '%s >%s %s' % (
                    self._type_desc, '='[ self._exclude_low: ], low )

        return '%s <%s %s <%s %s' % (
               low, '='[ self._exclude_low: ], self._type_desc,
               '='[ self._exclude_high: ], high )

    def create_editor ( self ):
        """ Returns the default UI editor for the trait.
        """
        # fixme: Needs to support a dynamic range editor.

        auto_set = self.auto_set
        if auto_set is None:
            auto_set = True

        from traitsui.api import RangeEditor

        return RangeEditor( self,
                            mode       = self.mode or 'auto',
                            cols       = self.cols or 3,
                            auto_set   = auto_set,
                            enter_set  = self.enter_set or False,
                            low_label  = self.low  or '',
                            high_label = self.high or '',
                            low_name   = self._low_name,
                            high_name  = self._high_name )


class Range ( BaseRange ):
    """ Defines a trait whose numeric value must be in a specified range using
        a C-level fast validator.
    """

    def init_fast_validator ( self, *args ):
        """ Set up the C-level fast validator.
        """
        self.fast_validate = args

#-------------------------------------------------------------------------------
#  'BaseEnum' and 'Enum' traits:
#-------------------------------------------------------------------------------

class BaseEnum ( TraitType ):
    """ Defines a trait whose value must be one of a specified set of values.
    """

    def __init__ ( self, *args, **metadata ):
        """ Returns an Enum trait.

        Parameters
        ----------
        values : list or tuple
            The enumeration of all legal values for the trait

        Default Value
        -------------
        values[0]
        """
        values = metadata.pop( 'values', None )
        if isinstance( values, basestring ):
            n = len( args )
            if n == 0:
                default_value = None
            elif n == 1:
                default_value = args[0]
            else:
                raise TraitError( "Incorrect number of arguments specified "
                                  "when using the 'values' keyword" )
            self.name   = values
            self.values = compile( 'object.' + values, '<string>', 'eval' )
            self.get, self.set, self.validate = self._get, self._set, None
        else:
            default_value = args[0]
            if (len( args ) == 1) and isinstance( default_value, SequenceTypes):
                args          = default_value
                default_value = args[0]
            elif (len( args ) == 2) and isinstance( args[1], SequenceTypes ):
                args = args[1]

            self.name   = ''
            self.values = tuple( args )
            self.init_fast_validator( 5, self.values )

        super( BaseEnum, self ).__init__( default_value, **metadata )

    def init_fast_validator ( self, *args ):
        """ Does nothing for the BaseEnum class. Used in the Enum class to set
            up the fast validator.
        """
        pass

    def validate ( self, object, name, value ):
        """ Validates that the value is one of the enumerated set of valid
            values.
        """
        if value in self.values:
            return value

        self.error( object, name, value )

    def full_info ( self, object, name, value ):
        """ Returns a description of the trait.
        """
        if self.name == '':
            values = self.values
        else:
            values = eval( self.values )

        return ' or '.join( [ repr( x ) for x in values ] )

    def create_editor ( self ):
        """ Returns the default UI editor for the trait.
        """
        from traitsui.api import EnumEditor

        values = self
        if self.name != '':
            values = None

        return EnumEditor( values   = values,
                           name     = self.name,
                           cols     = self.cols or 3,
                           evaluate = self.evaluate,
                           mode     = self.mode or 'radio' )

    def _get ( self, object, name, trait ):
        """ Returns the current value of a dynamic enum trait.
        """
        value  = self.get_value( object, name, trait )
        values = eval( self.values )
        if value not in values:
            value = None
            if len( values ) > 0:
                value = values[0]

        return value

    def _set ( self, object, name, value ):
        """ Sets the current value of a dynamic range trait.
        """
        if value in eval( self.values ):
            self.set_value( object, name, value )
        else:
            self.error( object, name, value )

class Enum ( BaseEnum ):
    """ Defines a trait whose value must be one of a specified set of values
        using a C-level fast validator.
    """

    def init_fast_validator ( self, *args ):
        """ Set up the C-level fast validator.
        """
        self.fast_validate = args

#-------------------------------------------------------------------------------
#  'BaseTuple' and 'Tuple' and 'ValidatedTuple' traits:
#-------------------------------------------------------------------------------

class BaseTuple ( TraitType ):
    """ Defines a trait whose value must be a tuple of specified trait types.
    """

    def __init__ ( self, *types, **metadata ):
        """ Returns a Tuple trait.

        Parameters
        ----------
        types : zero or more arguments
            Definition of the default and allowed tuples. If the first item of
            *types* is a tuple, it is used as the default value.
            The remaining argument list is used to form a tuple that constrains
            the  values assigned to the returned trait. The trait's value must
            be a tuple of the same length as the remaining argument list, whose
            elements must match the types specified by the corresponding items
            of the remaining argument list.

        Default Value
        -------------
        1. If no arguments are specified, the default value is ().
        2. If a tuple is specified as the first argument, it is the default
           value.
        3. If a tuple is not specified as the first argument, the default
           value is a tuple whose length is the length of the argument list,
           and whose values are the default values for the corresponding trait
           types.

        Example for case #2::

            mytuple = Tuple(('Fred', 'Betty', 5))

        The trait's value must be a 3-element tuple whose first and second
        elements are strings, and whose third element is an integer. The
        default value is ``('Fred', 'Betty', 5)``.

        Example for case #3::

            mytuple = Tuple('Fred', 'Betty', 5)

        The trait's value must be a 3-element tuple whose first and second
        elements are strings, and whose third element is an integer. The
        default value is ``('','',0)``.
        """
        if len( types ) == 0:
            self.init_fast_validator( 11, tuple, None, list )

            super( BaseTuple, self ).__init__( (), **metadata )

            return

        default_value = None

        if isinstance( types[0], tuple ):
            default_value, types = types[0], types[1:]
            if len( types ) == 0:
                types = [ Trait( element ) for element in default_value ]

        self.types = tuple( [ trait_from( type ) for type in types ] )
        self.init_fast_validator( 9, self.types )

        if default_value is None:
            default_value = tuple( [ type.default_value()[1]
                                     for type in self.types ] )

        super( BaseTuple, self ).__init__( default_value, **metadata )

    def init_fast_validator ( self, *args ):
        """ Saves the validation parameters.
        """
        self.no_type_check = (args[0] == 11)

    def validate ( self, object, name, value ):
        """ Validates that the value is a valid tuple.
        """
        if self.no_type_check:
            if isinstance( value, tuple ):
                return value

            if isinstance( value, list ):
                return tuple( value )

            self.error( object, name, value )

        try:
            if isinstance( value, list ):
                value = tuple( value )

            if isinstance( value, tuple ):
                types = self.types
                if len( value ) == len( types ):
                    values = []
                    for i, type in enumerate( types ):
                        values.append( type.validate( object, name, value[i] ) )

                    return tuple( values )
        except:
            pass

        self.error( object, name, value )

    def full_info ( self, object, name, value ):
        """ Returns a description of the trait.
        """
        if self.no_type_check:
            return 'a tuple'

        return 'a tuple of the form: (%s)' % (', '.join(
            [ type.full_info( object, name, value )
              for type in self.types ] ))

    def create_editor ( self ):
        """ Returns the default UI editor for the trait.
        """
        from traitsui.api import TupleEditor

        auto_set = self.auto_set
        if auto_set is None:
            auto_set = True
        enter_set = self.enter_set or False

        return TupleEditor( types     = self.types,
                            labels    = self.labels or [],
                            cols      = self.cols or 1,
                            auto_set  = auto_set,
                            enter_set = enter_set )

class Tuple ( BaseTuple ):
    """ Defines a trait whose value must be a tuple of specified trait types
        using a C-level fast validator.
    """

    def init_fast_validator ( self, *args ):
        """ Set up the C-level fast validator.
        """
        super( Tuple, self ).init_fast_validator( *args )

        self.fast_validate = args


class ValidatedTuple ( BaseTuple ):
    """ A Tuple trait that supports custom validation.
    """

    def __init__ ( self, *types, **metadata ):
        """ Returns a ValidatedTuple trait

        Parameters
        ----------
        types : zero or more arguments
            Definition of the default and allowed tuples. (see
            :class:`~.BaseTuple` for more details)
        fvalidate : callable, optional
            A callable to provide the additional custom validation for the
            tuple. The callable will be passed the tuple value and should
            return True or False.
        fvalidate_info : string, optional
            A string describing the custom validation to use for the error
            messages.

        For example::

          value_range = ValidatedTuple(Int(0), Int(1), fvalidate=lambda x: x[0] < x[1])

        This definition will accept only tuples ``(a, b)`` containing two integers
        that satisfy ``a < b``.
        """
        metadata.setdefault( 'fvalidate', None )
        metadata.setdefault( 'fvalidate_info', '' )
        super( ValidatedTuple, self ).__init__( *types, **metadata )

    def validate ( self, object, name, value ):
        """ Validates that the value is a valid tuple.
        """
        values = super( ValidatedTuple, self ).validate( object, name, value )
        # Exceptions in the fvalidate function will not result in a TraitError
        # but will be allowed to propagate up the frame stacks.
        if self.fvalidate is None or self.fvalidate( values ):
            return values
        else:
            self.error( object, name, value )

    def full_info ( self, object, name, value ):
        """ Returns a description of the trait.
        """
        message = 'a tuple of the form: ({0}) that passes custom validation{1}'
        types_info = ', '.join( [ type_.full_info( object, name, value )
                                  for type_ in self.types ] )
        if self.fvalidate_info is not None:
            fvalidate_info = ': {0}'.format( self.fvalidate_info )
        else:
            fvalidate_info = ''
        return message.format( types_info, fvalidate_info )

#-------------------------------------------------------------------------------
#  'List' trait:
#-------------------------------------------------------------------------------

class List ( TraitType ):
    """ Defines a trait whose value must be a list whose items are of the
        specified trait type.
    """

    info_trait         = None
    default_value_type = 5
    _items_event       = None

    def __init__ ( self, trait = None, value = None, minlen = 0,
                   maxlen = sys.maxint, items = True, **metadata ):
        """ Returns a List trait.

        Parameters
        ----------
        trait : a trait or value that can be converted to a trait using Trait()
            The type of item that the list contains. If not specified, the list
            can contain items of any type.
        value : list
            Default value for the list.
        minlen : integer
            The minimum length of a list that can be assigned to the trait.
        maxlen : integer
            The maximum length of a list that can be assigned to the trait.

        The length of the list assigned to the trait must be such that::

            minlen <= len(list) <= maxlen

        Default Value
        -------------
        *value* or None
        """
        metadata.setdefault( 'copy', 'deep' )

        if isinstance( trait, SequenceTypes ):
            trait, value = value, list( trait )

        if value is None:
            value = []

        self.item_trait = trait_from( trait )
        self.minlen     = max( 0, minlen )
        self.maxlen     = max( minlen, maxlen )
        self.has_items  = items

        if self.item_trait.instance_handler == '_instance_changed_handler':
            metadata.setdefault( 'instance_handler', '_list_changed_handler' )

        super( List, self ).__init__( value, **metadata )

    def validate ( self, object, name, value ):
        """ Validates that the values is a valid list.

        .. note::

            `object` can be None when validating a default value (see e.g.
            :meth:`~traits.trait_handlers.TraitType.clone`)

        """
        if (isinstance( value, list ) and
           (self.minlen <= len( value ) <= self.maxlen)):
            if object is None:
                return value

            return TraitListObject( self, object, name, value )

        self.error( object, name, value )

    def full_info ( self, object, name, value ):
        """ Returns a description of the trait.
        """
        if self.minlen == 0:
            if self.maxlen == sys.maxint:
                size = 'items'
            else:
                size = 'at most %d items' % self.maxlen
        else:
            if self.maxlen == sys.maxint:
                size = 'at least %d items' % self.minlen
            else:
                size = 'from %s to %s items' % (
                       self.minlen, self.maxlen )

        return 'a list of %s which are %s' % (
                   size, self.item_trait.full_info( object, name, value ) )

    def create_editor ( self ):
        """ Returns the default UI editor for the trait.
        """
        handler = self.item_trait.handler
        if isinstance( handler, TraitInstance ) and (self.mode != 'list'):
            from .api import HasTraits

            if issubclass( handler.aClass, HasTraits ):
                from traitsui.api import TableEditor

                return TableEditor()

        from traitsui.api import ListEditor

        return ListEditor( trait_handler = self,
                           rows          = self.rows or 5,
                           use_notebook  = self.use_notebook is True,
                           page_name     = self.page_name or '' )

    def inner_traits ( self ):
        """ Returns the *inner trait* (or traits) for this trait.
        """
        return ( self.item_trait, )

    #-- Private Methods --------------------------------------------------------

    def items_event ( self ):
        return items_event()

#-------------------------------------------------------------------------------
#  'CList' trait:
#-------------------------------------------------------------------------------

class CList ( List ):
    """ Defines a trait whose values must be a list whose items are of the
        specified trait type or which can be coerced to a list whose values are
        of the specified trait type.
    """

    def validate ( self, object, name, value ):
        """ Validates that the values is a valid list.
        """
        if not isinstance( value, list ):
            try:
                # Should work for all iterables as well as strings (which do
                # not define an __iter__ method)
                value = list( value )
            except (ValueError, TypeError):
                value = [ value ]

        return super( CList, self ).validate( object, name, value )

    def full_info ( self, object, name, value ):
        """ Returns a description of the trait.
        """
        return '%s or %s' % (
                   self.item_trait.full_info( object, name, value),
                   super( CList, self ).full_info( object, name, value ) )

#-------------------------------------------------------------------------------
#  'Set' trait:
#-------------------------------------------------------------------------------

class Set ( TraitType ):
    """ Defines a trait whose value must be a set whose items are of the
        specified trait type.
    """

    info_trait         = None
    default_value_type = 9
    _items_event       = None

    def __init__ ( self, trait = None, value = None, items = True, **metadata ):
        """ Returns a Set trait.

        Parameters
        ----------
        trait : a trait or value that can be converted to a trait using Trait()
            The type of item that the list contains. If not specified, the list
            can contain items of any type.
        value : set
            Default value for the set.

        Default Value
        -------------
        *value* or None
        """
        metadata.setdefault( 'copy', 'deep' )

        if isinstance( trait, SetTypes ):
            trait, value = value, set( trait )

        if value is None:
            value = set()

        self.item_trait = trait_from( trait )
        self.has_items  = items

        super( Set, self ).__init__( value, **metadata )

    def validate ( self, object, name, value ):
        """ Validates that the values is a valid set.

        .. note::

            `object` can be None when validating a default value (see e.g.
            :meth:`~traits.trait_handlers.TraitType.clone`)

        """
        if isinstance( value, set ):
            if object is None:
                return value

            return TraitSetObject( self, object, name, value )

        self.error( object, name, value )

    def full_info ( self, object, name, value ):
        """ Returns a description of the trait.
        """
        return 'a set of %s' % self.item_trait.full_info( object, name, value )

    def create_editor ( self ):
        """ Returns the default UI editor for the trait.
        """
        # fixme: Needs to be customized for sets.
        handler = self.item_trait.handler
        if isinstance( handler, TraitInstance ) and (self.mode != 'list'):
            from .api import HasTraits

            if issubclass( handler.aClass, HasTraits ):
                try:
                    object = handler.aClass()
                    from traitsui.table_column import ObjectColumn
                    from traitsui.table_filter import (EvalFilterTemplate,
                        RuleFilterTemplate, MenuFilterTemplate, EvalTableFilter)
                    from traitsui.api import TableEditor

                    return TableEditor(
                            columns = [ ObjectColumn( name = name )
                                        for name in object.editable_traits() ],
                            filters     = [ RuleFilterTemplate,
                                            MenuFilterTemplate,
                                            EvalFilterTemplate ],
                            edit_view   = '',
                            orientation = 'vertical',
                            search      = EvalTableFilter(),
                            deletable   = True,
                            row_factory = handler.aClass )
                except:
                    pass

        from traitsui.api import ListEditor

        return ListEditor( trait_handler = self,
                           rows          = self.rows or 5,
                           use_notebook  = self.use_notebook is True,
                           page_name     = self.page_name or '' )

    def inner_traits ( self ):
        """ Returns the *inner trait* (or traits) for this trait.
        """
        return ( self.item_trait, )

    #-- Private Methods --------------------------------------------------------

    def items_event ( self ):
        if self.__class__._items_event is None:
            self.__class__._items_event = \
                Event( TraitSetEvent, is_base = False ).as_ctrait()

        return self.__class__._items_event

#-------------------------------------------------------------------------------
#  'CSet' trait:
#-------------------------------------------------------------------------------

class CSet ( Set ):
    """ Defines a trait whose values must be a set whose items are of the
        specified trait type or which can be coerced to a set whose values are
        of the specified trait type.
    """

    def validate ( self, object, name, value ):
        """ Validates that the values is a valid list.
        """
        if not isinstance( value, set ):
            try:
                # Should work for all iterables as well as strings (which do
                # not define an __iter__ method)
                value = set( value )
            except ( ValueError, TypeError ):
                value = set( [ value ] )

        return super( CSet, self ).validate( object, name, value )

    def full_info ( self, object, name, value ):
        """ Returns a description of the trait.
        """
        return '%s or %s' % (
                   self.item_trait.full_info( object, name, value),
                   super( CSet, self ).full_info( object, name, value ) )

#-------------------------------------------------------------------------------
#  'Dict' trait:
#-------------------------------------------------------------------------------

class Dict ( TraitType ):
    """ Defines a trait whose value must be a dictionary, optionally with
        specified types for keys and values.
    """

    info_trait         = None
    default_value_type = 6
    _items_event       = None

    def __init__ ( self, key_trait = None, value_trait = None, value = None,
                   items = True, **metadata ):
        """ Returns a Dict trait.

        Parameters
        ----------
        key_trait : a trait or value that can convert to a trait using Trait()
            The trait type for keys in the dictionary; if not specified, any
            values can be used as keys.
        value_trait : a trait or value that can convert to a trait using Trait()
            The trait type for values in the dictionary; if not specified, any
            values can be used as dictionary values.
        value : dict
            The default value for the returned trait.
        items : bool
            Indicates whether the value contains items.

        Default Value
        -------------
        *value* or {}
        """
        if isinstance( key_trait, dict ):
            key_trait, value_trait, value = value_trait, value, key_trait

        if value is None:
            value = {}

        self.key_trait   = trait_from( key_trait )
        self.value_trait = trait_from( value_trait )
        self.has_items   = items

        handler = self.value_trait.handler
        if (handler is not None) and handler.has_items:
            handler = handler.clone()
            handler.has_items = False
        self.value_handler = handler

        super( Dict, self ).__init__( value, **metadata )

    def validate ( self, object, name, value ):
        """ Validates that the value is a valid dictionary.

        .. note::

            `object` can be None when validating a default value (see e.g.
            :meth:`~traits.trait_handlers.TraitType.clone`)

        """
        if isinstance( value, dict ):
            if object is None:
                return value
            return TraitDictObject( self, object, name, value )

        self.error( object, name, value )

    def full_info ( self, object, name, value ):
        """ Returns a description of the trait.
        """
        return ('a dictionary with keys which are %s and with values which '
                'are %s') % (
                self.key_trait.full_info(   object, name, value ),
                self.value_trait.full_info( object, name, value ) )

    def create_editor ( self ):
        """ Returns the default UI editor for the trait.
        """
        from traitsui.api import TextEditor

        return TextEditor( evaluate = eval )

    def inner_traits ( self ):
        """ Returns the *inner trait* (or traits) for this trait.
        """
        return ( self.key_trait, self.value_trait )

    #-- Private Methods --------------------------------------------------------

    def items_event ( self ):
        cls = self.__class__
        if cls._items_event is None:
            cls._items_event = \
                Event( TraitDictEvent, is_base = False ).as_ctrait()

        return cls._items_event

#-------------------------------------------------------------------------------
#  'BaseInstance' and 'Instance' traits:
#-------------------------------------------------------------------------------

# Allowed values and mappings for the 'adapt' keyword:
AdaptMap = {
   'no':      0,
   'yes':     1,
   'default': 2
}

class BaseClass ( TraitType ):
    """ Base class for types which have an associated class which can be
        determined dynamically by specifying a string name for the class (e.g.
        'package1.package2.module.class'.

        Any subclass must define instances with 'klass' and 'module' attributes
        that contain the string name of the class (or actual class object) and
        the module name that contained the original trait definition (used for
        resolving local class names (e.g. 'LocalClass')).

        This is an abstract class that only provides helper methods used to
        resolve the class name into an actual class object.
    """

    def resolve_class ( self, object, name, value ):
        klass = self.validate_class( self.find_class( self.klass ) )
        if klass is None:
            self.validate_failed( object, name, value )

        self.klass = klass

    def validate_class ( self, klass ):
        return klass

    def find_class ( self, klass ):
        module = self.module
        col    = klass.rfind( '.' )
        if col >= 0:
            module = klass[ : col ]
            klass = klass[ col + 1: ]

        theClass = getattr( sys.modules.get( module ), klass, None )
        if (theClass is None) and (col >= 0):
            try:
                mod = __import__( module )
                for component in module.split( '.' )[1:]:
                    mod = getattr( mod, component )

                theClass = getattr( mod, klass, None )
            except:
                pass

        return theClass

    def validate_failed ( self, object, name, value ):

        self.error( object, name, value )

def validate_implements ( value, klass, unused = None ):
    """ Checks to see if a specified value implements the instance class
        interface (if it is an interface).
    """

    from .has_traits import isinterface
    from .interface_checker import check_implements

    return isinterface(klass) and check_implements( value.__class__, klass )

#: Tell the C-base code about the 'validate_implements' function (used by the
#: 'fast_validate' code for Instance types):
from . import ctraits
ctraits._validate_implements( validate_implements )

class BaseInstance ( BaseClass ):
    """ Defines a trait whose value must be an instance of a specified class,
        or one of its subclasses.
    """

    adapt_default = 'no'

    def __init__ ( self, klass = None, factory = None, args = None, kw = None,
                   allow_none = True, adapt = None, module = None,
                   **metadata ):
        """ Returns an Instance trait.

        Parameters
        ----------
        klass : class or instance
            The object that forms the basis for the trait; if it is an
            instance, then trait values must be instances of the same class or
            a subclass. This object is not the default value, even if it is an
            instance.
        factory : callable
            A callable, typically a class, that when called with *args* and
            *kw*, returns the default value for the trait. If not specified,
            or *None*, *klass* is used as the factory.
        args : tuple
            Positional arguments for generating the default value.
        kw : dictionary
            Keyword arguments for generating the default value.
        allow_none : bool
            Indicates whether None is allowed as a value.
        adapt : str
            A string specifying how adaptation should be applied. The possible
            values are:

                - 'no': Adaptation is not allowed.
                - 'yes': Adaptation is allowed. If adaptation fails, an
                    exception should be raised.
                - 'default': Adaptation is allowed. If adaptation fails, the
                    default value for the trait should be used.

        Default Value
        -------------
        **None** if *klass* is an instance or if it is a class and *args* and
        *kw* are not specified. Otherwise, the default value is the instance
        obtained by calling ``klass(*args, **kw)``. Note that the constructor
        call is performed each time a default value is assigned, so each
        default value assigned is a unique instance.
        """
        if klass is None:
            raise TraitError( 'A %s trait must have a class specified.' %
                              self.__class__.__name__ )

        metadata.setdefault( 'copy', 'deep' )
        metadata.setdefault( 'instance_handler', '_instance_changed_handler' )

        adapt = adapt or self.adapt_default
        if adapt not in AdaptMap:
            raise TraitError( "'adapt' must be 'yes', 'no' or 'default'." )

        if isinstance( factory, tuple ):
            if args is None:
                args, factory = factory, klass
            elif isinstance( args, dict ):
                factory, args, kw = klass, factory, args

        elif (kw is None) and isinstance( factory, dict ):
            kw, factory = factory, klass

        elif ((args is not None) or (kw is not None)) and (factory is None):
            factory = klass

        self._allow_none = allow_none
        self.adapt       = AdaptMap[ adapt ]
        self.module      = module or get_module_name()

        if isinstance( klass, basestring ):
            self.klass = klass
        else:
            if not isinstance( klass, ClassTypes ):
                klass = klass.__class__

            self.klass = klass
            self.init_fast_validate()

        value = factory
        if factory is not None:
            if args is None:
                args = ()

            if kw is None:
                if isinstance( args, dict ):
                    kw   = args
                    args = ()
                else:
                    kw = {}
            elif not isinstance( kw, dict ):
                raise TraitError( "The 'kw' argument must be a dictionary." )

            if ((not callable( factory )) and
                (not isinstance( factory, basestring ))):
                if (len( args ) > 0) or (len( kw ) > 0):
                    raise TraitError( "'factory' must be callable" )
            else:
                value = _InstanceArgs( factory, args, kw )

        self.default_value = value

        super( BaseInstance, self ).__init__( value, **metadata )

    def validate ( self, object, name, value ):
        """ Validates that the value is a valid object instance.
        """
        from traits.adaptation.api import adapt

        if value is None:
            if self._allow_none:
                return value

            self.validate_failed( object, name, value )

        if isinstance( self.klass, basestring ):
            self.resolve_class( object, name, value )

        if self.adapt == 0:
            try:
                if value is adapt( value, self.klass ):
                    return value
            except:
                if validate_implements( value, self.klass ):
                    return value

        elif self.adapt == 1:
            try:
                return adapt( value, self.klass )
            except:
                if validate_implements( value, self.klass ):
                    return value

        else:
            result = adapt( value, self.klass, None )
            if result is None:
                if validate_implements( value, self.klass ):
                    return value

                result = self.default_value
                if isinstance( result, _InstanceArgs ):
                    result = result[0]( *result[1], **result[2] )

            return result

        self.validate_failed( object, name, value )

    def info ( self ):
        """ Returns a description of the trait.
        """
        klass = self.klass
        if not isinstance( klass, basestring ):
            klass = klass.__name__

        if self.adapt == 0:
            result = class_of( klass )
        else:
            result = ('an implementor of, or can be adapted to implement, %s' %
                      klass)

        if self._allow_none:
            return result + ' or None'

        return result

    def get_default_value ( self ):
        """ Returns a tuple of the form: ( default_value_type, default_value )
            which describes the default value for this trait.
        """
        dv  = self.default_value
        dvt = self.default_value_type
        if dvt < 0:
            if not isinstance( dv, _InstanceArgs ):
                return super( BaseInstance, self ).get_default_value()

            self.default_value_type = dvt = 7
            self.default_value      = dv  = ( self.create_default_value,
                                              dv.args, dv.kw )

        return ( dvt, dv )

    def create_editor ( self ):
        """ Returns the default traits UI editor for this type of trait.
        """
        from traitsui.api import InstanceEditor

        return InstanceEditor( label = self.label or '',
                               view  = self.view  or '',
                               kind  = self.kind  or 'live' )

    #-- Private Methods --------------------------------------------------------

    def create_default_value ( self, *args, **kw ):
        klass = args[0]
        if isinstance( klass, basestring ):
            klass = self.validate_class( self.find_class( klass ) )
            if klass is None:
                raise TraitError, 'Unable to locate class: ' + args[0]

        return klass( *args[1:], **kw )

    #: fixme: Do we still need this method using the new style?...
    def allow_none ( self ):
        self._allow_none = True
        self.init_fast_validate()

    def init_fast_validate ( self ):
        """ Does nothing for the BaseInstance' class. Used by the 'Instance',
            'AdaptedTo' and 'AdaptsTo' classes to set up the C-level fast
            validator.
        """
        pass

    def resolve_class ( self, object, name, value ):
        super( BaseInstance, self ).resolve_class( object, name, value )

        #: fixme: The following is quite ugly, because it wants to try and fix
        #: the trait referencing this handler to use the 'fast path' now that the
        #: actual class has been resolved. The problem is finding the trait,
        # especially in the case of List(Instance('foo')), where the
        # object.base_trait(...) value is the List trait, not the Instance
        # trait, so we need to check for this and pull out the List
        # 'item_trait'. Obviously this does not extend well to other traits
        # containing nested trait references (Dict?)...
        self.init_fast_validate()
        trait   = object.base_trait( name )
        handler = trait.handler
        if handler is not self:
            set_validate = getattr( handler, 'set_validate', None )
            if set_validate is not None:
                # The outer trait is a TraitCompound. Recompute its
                # fast_validate table now that we have updated ours.
                # FIXME: there are probably still issues if the TraitCompound is
                # further nested.
                set_validate()
            else:
                item_trait = getattr( handler, 'item_trait', None )
                if item_trait is not None and item_trait.handler is self:
                    # The outer trait is a List trait.
                    trait   = item_trait
                    handler = self
                else:
                    return
        if handler.fast_validate is not None:
            trait.set_validate( handler.fast_validate )

class Instance ( BaseInstance ):
    """ Defines a trait whose value must be an instance of a specified class,
        or one of its subclasses using a C-level fast validator.
    """

    def init_fast_validate ( self ):
        """ Sets up the C-level fast validator. """

        from .has_traits import isinterface

        if (self.adapt == 0) and (not isinterface(self.klass)):
            fast_validate = [ 1, self.klass ]
            if self._allow_none:
                fast_validate = [ 1, None, self.klass ]

            if self.klass in TypeTypes:
                fast_validate[0] = 0

            self.fast_validate = tuple( fast_validate )
        else:
            self.fast_validate = ( 19, self.klass, self.adapt,
                                   self._allow_none )

class Supports( Instance ):
    """ A traits whose value must support a specified protocol.

    In other words, the value of the trait directly provide, or can be adapted
    to, the given protocol (Interface or type).

    The value of the trait after assignment is the possibly adapted value
    (i.e., it is the original assigned value if that provides the protocol,
    or is an adapter otherwise).

    The original, unadapted value is stored in a "shadow" attribute with
    the same name followed by an underscore (e.g., ``foo`` and ``foo_``).
    """

    adapt_default = 'yes'

    def post_setattr ( self, object, name, value ):
        """ Performs additional post-assignment processing.
        """
        # Save the original, unadapted value in the mapped trait:
        object.__dict__[ name + '_' ] = value

    def as_ctrait ( self ):
        """ Returns a CTrait corresponding to the trait defined by this class.
        """
        return self.modify_ctrait( super( AdaptedTo, self ).as_ctrait() )

    def modify_ctrait ( self, ctrait ):

        # Tell the C code that the 'post_setattr' method wants the original,
        # unadapted value passed to 'setattr':
        return ctrait.post_setattr_original_value( True )

# Alias defined for backward compatibility with Traits 4.3.0
AdaptedTo = Supports

class AdaptsTo ( Supports ):
    """ A traits whose value must support a specified protocol.

    In other words, the value of the trait directly provide, or can be adapted
    to, the given protocol (Interface or type).

    The value of the trait after assignment is the original, unadapted value.

    A possibly adapted value is stored in a "shadow" attribute with
    the same name followed by an underscore (e.g., ``foo`` and ``foo_``).
    """

    def modify_ctrait ( self, ctrait ):
        # Tell the C code that 'setattr' should store the original, unadapted
        # value passed to it:
        return ctrait.setattr_original_value( True )

#-------------------------------------------------------------------------------
#  'Type' trait:
#-------------------------------------------------------------------------------

class Type ( BaseClass ):
    """ Defines a trait whose value must be a subclass of a specified class.
    """

    def __init__ ( self, value = None, klass = None, allow_none = True,
                         **metadata ):
        """ Returns an Type trait.

        Parameters
        ----------
        value : class or None

        klass : class or None

        allow_none : bool
            Indicates whether None is allowed as an assignable value. Even if
            **False**, the default *value* may be **None**.

        Default Value
        -------------
        **None** if *klass* is an instance or if it is a class and *args* and
        *kw* are not specified. Otherwise, the default value is the instance
        obtained by calling ``klass(*args, **kw)``. Note that the constructor
        call is performed each time a default value is assigned, so each
        default value assigned is a unique instance.
        """
        if value is None:
            if klass is None:
                klass = object

        elif klass is None:
            klass = value

        if isinstance( klass, basestring ):
            self.validate = self.resolve

        elif not isinstance( klass, ClassTypes ):
            raise TraitError( "A Type trait must specify a class." )

        self.klass       = klass
        self._allow_none = allow_none
        self.module      = get_module_name()

        super( Type, self ).__init__( value, **metadata )

    def validate ( self, object, name, value ):
        """ Validates that the value is a valid object instance.
        """
        try:
            if issubclass( value, self.klass ):
                return value
        except:
            if (value is None) and (self._allow_none):
                return value

        self.error( object, name, value )

    def resolve ( self, object, name, value ):
        """ Resolves a class originally specified as a string into an actual
            class, then resets the trait so that future calls will be handled by
            the normal validate method.
        """
        if isinstance( self.klass, basestring ):
            self.resolve_class( object, name, value )
            del self.validate

        return self.validate( object, name, value )

    def info ( self ):
        """ Returns a description of the trait.
        """
        klass = self.klass
        if not isinstance( klass, basestring ):
            klass = klass.__name__

        result = 'a subclass of ' + klass

        if self._allow_none:
            return result + ' or None'

        return result

    def get_default_value ( self ):
        """ Returns a tuple of the form: ( default_value_type, default_value )
            which describes the default value for this trait.
        """
        if not isinstance( self.default_value, basestring ):
            return super( Type, self ).get_default_value()

        return ( 7, ( self.resolve_default_value, (), None ) )

    def resolve_default_value ( self ):
        """ Resolves a class name into a class so that it can be used to
            return the class as the default value of the trait.
        """
        if isinstance( self.klass, basestring ):
            try:
                self.resolve_class( None, None, None )
                del self.validate
            except:
                raise TraitError( 'Could not resolve %s into a valid class' %
                                  self.klass )

        return self.klass

#-------------------------------------------------------------------------------
#  'Event' trait:
#-------------------------------------------------------------------------------

class Event ( TraitType ):

    def __init__ ( self, trait = None, **metadata ):
        metadata[ 'type' ]      = 'event'
        metadata[ 'transient' ] = True

        super( Event, self ).__init__( **metadata )

        self.trait = None
        if trait is not None:
            self.trait = trait_from( trait )
            validate   = self.trait.get_validate()
            if validate is not None:
                self.fast_validate = validate

    def full_info ( self, object, name, value ):
        """ Returns a description of the trait.
        """
        trait = self.trait
        if trait is None:
            return 'any value'

        return trait.full_info( object, name, value )

#  Handle circular module dependencies:
trait_handlers.Event = Event

#-------------------------------------------------------------------------------
#  'Button' trait:
#-------------------------------------------------------------------------------

class Button ( Event ):
    """ Defines a trait whose UI editor is a button.
    """

    def __init__ ( self, label = '', image = None, values_trait = None, style = 'button',
                         orientation = 'vertical', width_padding = 7,
                         height_padding = 5, view = None, **metadata ):
        """ Returns a trait event whose editor is a button.

            Parameters
            ----------
            label : str
                The label for the button.
            image : pyface.ImageResource
                An image to display on the button.
            style : one of: 'button', 'radio', 'toolbar', 'checkbox'
                The style of button to display.
            values_trait : str
                For a "button" or "toolbar" style, the name of an enum
                trait whose values will populate a drop-down menu on the button.
                The selected value will replace the label on the button.
            orientation : one of: 'horizontal', 'vertical'
                The orientation of the label relative to the image.
            width_padding : integer between 0 and 31
                Extra padding (in pixels) added to the left and right sides of
                the button.
            height_padding : integer between 0 and 31
                Extra padding (in pixels) added to the top and bottom of the
                button.

            Default Value
            -------------
            No default value because events do not store values.
        """
        self.label = label
        self.values_trait = values_trait
        self.image = image
        self.style = style
        self.orientation = orientation
        self.width_padding = width_padding
        self.height_padding = height_padding
        self.view = view
        super( Button, self ).__init__( **metadata )

    def create_editor(self):
        from traitsui.api import ButtonEditor

        editor = ButtonEditor(
            label = self.label,
            values_trait = self.values_trait,
            image = self.image,
            style = self.style,
            orientation = self.orientation,
            width_padding = self.width_padding,
            height_padding = self.height_padding,
            view = self.view,
        )
        return editor


#-------------------------------------------------------------------------------
#  'ToolbarButton' trait:
#-------------------------------------------------------------------------------

class ToolbarButton ( Button ):
    """ Defines a trait whose UI editor is a button that can be used on a
        toolbar.
    """

    def __init__ ( self, label = '', image = None, style = 'toolbar',
                         orientation = 'vertical', width_padding = 2,
                         height_padding = 2, **metadata ):
        """ Returns a trait event whose editor is a toolbar button.

            Parameters
            ----------
            label : str
                The label for the button
            image : pyface.ImageResource
                An image to display on the button
            style : one of: 'button', 'radio', 'toolbar', 'checkbox'
                The style of button to display
            orientation : one of ['horizontal', 'vertical']
                The orientation of the label relative to the image
            width_padding : integer between 0 and 31
                Extra padding (in pixels) added to the left and right sides of
                the button
            height_padding : integer between 0 and 31
                Extra padding (in pixels) added to the top and bottom of the
                button

            Default Value
            -------------
            No default value because events do not store values.

        """
        super( ToolbarButton, self ).__init__( label,
                                               image=image,
                                               style=style,
                                               orientation=orientation,
                                               width_padding=width_padding,
                                               height_padding=height_padding,
                                               **metadata )

#-------------------------------------------------------------------------------
#  'Either' trait:
#-------------------------------------------------------------------------------

class Either ( TraitType ):
    """ Defines a trait whose value can be any of of a specified list of traits.
    """

    def __init__ ( self, *traits, **metadata ):
        """ Creates a trait whose value can be any of of a specified list of
            traits.
        """
        self.trait_maker = _TraitMaker( metadata.pop( 'default', None ),
                                        *traits, **metadata )

    def as_ctrait ( self ):
        """ Returns a CTrait corresponding to the trait defined by this class.
        """
        return self.trait_maker.as_ctrait()

#-------------------------------------------------------------------------------
#  'Symbol' trait:
#-------------------------------------------------------------------------------

class Symbol ( TraitType ):

    #: A description of the type of value this trait accepts:
    info_text = ("an object or a string of the form "
        "'[package.package...package.]module[:symbol[([arg1,...,argn])]]' "
        "specifying where to locate the object")

    def get ( self, object, name ):
        value = object.__dict__.get( name, Undefined )
        if value is Undefined:
            cache = TraitsCache + name
            ref   = object.__dict__.get( cache )
            if ref is None:
                object.__dict__[ cache ] = ref = \
                    object.trait( name ).default_value_for( object, name )

            if isinstance( ref, basestring ):
                object.__dict__[ name ] = value = self._resolve( ref )

        return value

    def set ( self, object, name, value ):
        dict = object.__dict__
        old  = dict.get( name, Undefined )
        if isinstance( value, basestring ):
            dict.pop( name, None )
            dict[ TraitsCache + name ] = value
            object.trait_property_changed( name, old )
        else:
            dict[ name ] = value
            object.trait_property_changed( name, old, value )

    def _resolve ( self, ref ):
        try:
            path   = ref.split( ':', 1 )
            module = __import__( path[0] )
            for component in path[0].split( '.' )[1:]:
                module = getattr( module, component )

            if len( path ) == 1:
                return module

            elements = path[1].split( '(', 1 )
            symbol   = getattr( module, elements[0] )
            if len( elements ) == 1:
                return symbol

            args = eval( '(' + elements[1] )
            if not isinstance( args, tuple ):
                args = ( args, )

            return symbol( *args )
        except:
            raise TraitError( "Could not resolve '%s' into a valid symbol." %
                              ref )


if python_version >= 2.5:

    import uuid

    #---------------------------------------------------------------------------
    #  'UUID' trait:
    #---------------------------------------------------------------------------

    class UUID ( TraitType ):
        """ Defines a trait whose value is a globally unique UUID (type 4).
        """

        #: A description of the type of value this trait accepts:
        info_text = 'a read-only UUID'

        def __init__ ( self, **metadata ):
            """ Returns a UUID trait.
            """
            super( UUID, self ).__init__( None, **metadata )

        def validate ( self, object, name, value ):
            """ Raises an error, since no values can be assigned to the trait.
            """
            raise TraitError( "The '%s' trait of %s instance is a read-only "
                              "UUID." % ( name, class_of( object ) ) )

        def get_default_value ( self ):
            return ( 7, ( self._create_uuid, (), None ) )

        #-- Private Methods ---------------------------------------------------

        def _create_uuid ( self ):
            return uuid.uuid4()

#-------------------------------------------------------------------------------
#  'WeakRef' trait:
#-------------------------------------------------------------------------------

class WeakRef ( Instance ):
    """ Returns a trait whose value must be an instance of the same type
    (or a subclass) of the specified *klass*, which can be a class or an
    instance. Note that the trait only maintains a weak reference to the
    assigned value.
    """

    def __init__ ( self, klass = 'traits.has_traits.HasTraits',
                         allow_none = False, adapt = 'yes', **metadata ):
        """ Returns a WeakRef trait.

        Only a weak reference is maintained to any object assigned to a WeakRef
        trait. If no other references exist to the assigned value, the value
        may be garbage collected, in which case the value of the trait becomes
        None. In all other cases, the value returned by the trait is the
        original object.

        Parameters
        ----------
        klass : class or instance
            The object that forms the basis for the trait. If *klass* is
            omitted, then values must be an instance of HasTraits.
        allow_none : boolean
            Indicates whether None can be assigned.

        Default Value
        -------------
        **None** (even if allow_none==False)
        """

        metadata.setdefault( 'copy', 'ref' )

        super( WeakRef, self ).__init__( klass, allow_none = allow_none,
                         adapt = adapt, module = get_module_name(), **metadata )

    def get ( self, object, name ):
        value = getattr( object, name + '_', None )
        if value is not None:
            return value.value()

        return None

    def set ( self, object, name, value ):
        old = self.get( object, name )

        if value is None:
            object.__dict__[ name + '_' ] = None
        else:
            object.__dict__[ name + '_' ] = HandleWeakRef( object, name, value )

        if value is not old:
            object.trait_property_changed( name, old, value )

    def resolve_class ( self, object, name, value ):
        # fixme: We have to override this method to prevent the 'fast validate'
        # from being set up, since the trait using this is a 'property' style
        # trait which is not currently compatible with the 'fast_validate'
        # style (causes internal Python SystemError messages).
        klass = self.find_class( self.klass )
        if klass is None:
            self.validate_failed( object, name, value )

        self.klass = klass


#-- Date Trait definition ----------------------------------------------------
Date = BaseInstance(datetime.date, editor=date_editor)


#-- Time Trait definition ----------------------------------------------------
Time = BaseInstance(datetime.time, editor=time_editor)


#-------------------------------------------------------------------------------
#  Create predefined, reusable trait instances:
#-------------------------------------------------------------------------------

# Synonym for Bool; default value is False.
false = Bool

# Boolean values only; default value is True.
true = Bool( True )

# Allows any value to be assigned; no type-checking is performed.
# Default value is Undefined.
undefined = Any( Undefined )

#-- List Traits ----------------------------------------------------------------

#: List of integer values; default value is [].
ListInt = List( int )

#: List of float values; default value is [].
ListFloat = List( float )

#: List of string values; default value is [].
ListStr = List( str )

#: List of Unicode string values; default value is [].
ListUnicode = List( unicode )

#: List of complex values; default value is [].
ListComplex = List( complex )

#: List of Boolean values; default value is [].
ListBool = List( bool )

#: List of function values; default value is [].
ListFunction = List( FunctionType )

#: List of method values; default value is [].
ListMethod = List( MethodType )

if sys.version_info[0] < 3:
    from types import ClassType, InstanceType

    #: List of class values; default value is [].
    ListClass = List( ClassType )

    #: List of instance values; default value is [].
    ListInstance = List( InstanceType )

#: List of container type values; default value is [].
ListThis = List( ThisClass )

#-- Dictionary Traits ----------------------------------------------------------

#: Only a dictionary of string:Any values can be assigned; only string keys can
#: be inserted. The default value is {}.
DictStrAny = Dict( str, Any )

#: Only a dictionary of string:string values can be assigned; only string keys
#: with string values can be inserted. The default value is {}.
DictStrStr = Dict( str, str )

#: Only a dictionary of string:integer values can be assigned; only string keys
#: with integer values can be inserted. The default value is {}.
DictStrInt = Dict( str, int )

#: Only a dictionary of string:long-integer values can be assigned; only string
#: keys with long-integer values can be inserted. The default value is {}.
DictStrLong = Dict( str, long )

#: Only a dictionary of string:float values can be assigned; only string keys
#: with float values can be inserted. The default value is {}.
DictStrFloat = Dict( str, float )

#: Only a dictionary of string:bool values can be assigned; only string keys
#: with boolean values can be inserted. The default value is {}.
DictStrBool = Dict( str, bool )

#: Only a dictionary of string:list values can be assigned; only string keys
#: with list values can be assigned. The default value is {}.
DictStrList = Dict( str, list )
