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trait_base.py

#------------------------------------------------------------------------------
# Copyright (c) 2005, 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: 06/21/2002
#
#  Symbols defined: SequenceTypes
#                   Undefined
#                   trait_editors
#                   class_of
#
#  Refactored into a separate module: 07/04/2003
#------------------------------------------------------------------------------

#-------------------------------------------------------------------------------
#  Imports:
#-------------------------------------------------------------------------------
""" Defines common, low-level capabilities needed by the Traits package.
"""
from __future__ import generators

import os
import sys

from os.path import exists, join
from string  import lowercase, uppercase
from types   import ListType, TupleType, DictType, StringType, UnicodeType, \
                    IntType, LongType, FloatType, ComplexType, ClassType, \
                    TypeType

from enthought.etsconfig.api import ETSConfig

#-------------------------------------------------------------------------------
#  Provide Python 2.3+ compatible definitions (if necessary):
#-------------------------------------------------------------------------------

try:
    from types import BooleanType
except ImportError:
    BooleanType = IntType

def _enumerate ( seq ):
    for i in xrange( len( seq) ):
        yield i, seq[i]
try:
    enumerate = enumerate
except:
    enumerate = _enumerate
del _enumerate

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

ClassTypes    = ( ClassType, TypeType )

SequenceTypes = ( ListType, TupleType )

ComplexTypes  = ( float, int )

TypeTypes     = ( StringType,   UnicodeType,  IntType,    LongType,
                  FloatType,    ComplexType,  ListType,   TupleType,
                  DictType,     BooleanType )

TraitNotifier = '__trait_notifier__'

#-------------------------------------------------------------------------------
#  Singleton 'Undefined' object (used as undefined trait name and/or value):
#-------------------------------------------------------------------------------

class _Undefined ( object ):

   def __repr__ ( self ):
       return '<undefined>'

# Singleton object that indicates that a trait attribute has not yet had a
# value set (i.e., its value is undefined. This object is used instead of
# None, because None is often has other meanings, such as that a value
# is not used. When a trait attribute is first assigned a value, and its
# associated trait notification handlers are called, Undefined is passed
# as the *old* parameter, to indicate that the attribute previously had no
# value.
Undefined = _Undefined()

# Tell the C-base code about the 'Undefined' objects:
import ctraits
ctraits._undefined( Undefined )

#-------------------------------------------------------------------------------
#  Singleton 'Missing' object (used as missing method argument marker):
#-------------------------------------------------------------------------------

class _Missing ( object ):

   def __repr__ ( self ):
       return '<missing>'

# Singleton object that indicates that a method argument is missing from a
# type-checked method signature.
Missing = _Missing()

#-------------------------------------------------------------------------------
#  Singleton 'Self' object (used as object reference to current 'object'):
#-------------------------------------------------------------------------------

class _Self ( object ):

   def __repr__ ( self ):
       return '<self>'

# Singleton object that references the current 'object'.
Self = _Self()

#-------------------------------------------------------------------------------
#  Define a special 'string' coercion function:
#-------------------------------------------------------------------------------

def strx ( arg ):
    """ Wraps the built-in str() function to raise a TypeError if the
    argument is not of a type in StringTypes.
    """
    if type( arg ) in StringTypes:
       return str( arg )
    raise TypeError

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

StringTypes  = ( StringType, UnicodeType, IntType, LongType, FloatType,
                 ComplexType )

#-------------------------------------------------------------------------------
#  Define a mapping of coercable types:
#-------------------------------------------------------------------------------

# Mapping of coercable types.
CoercableTypes = {
    LongType:    ( 11, long, int ),
    FloatType:   ( 11, float, int ),
    ComplexType: ( 11, complex, float, int ),
    UnicodeType: ( 11, unicode, str )
}

#-------------------------------------------------------------------------------
#  Return a string containing the class name of an object with the correct
#  article (a or an) preceding it (e.g. 'an Image', 'a PlotValue'):
#-------------------------------------------------------------------------------

def class_of ( object ):
    """ Returns a string containing the class name of an object with the
    correct indefinite article ('a' or 'an') preceding it (e.g., 'an Image',
    'a PlotValue').
    """
    if isinstance(object, basestring):
       return add_article( object )
    return add_article( object.__class__.__name__ )

#-------------------------------------------------------------------------------
#  Return a string containing the right article (i.e. 'a' or 'an') prefixed to
#  a specified string:
#-------------------------------------------------------------------------------

def add_article ( name ):
    """ Returns a string containing the correct indefinite article ('a' or 'an')
    prefixed to the specified string.
    """
    if name[:1].lower() in 'aeiou':
       return 'an ' + name
    return 'a ' + name

#----------------------------------------------------------------------------
#  Return a 'user-friendly' name for a specified trait:
#----------------------------------------------------------------------------

def user_name_for ( name ):
    """ Returns a "user-friendly" version of a string, with the first letter
    capitalized and with underscore characters replaced by spaces. For example,
    ``user_name_for('user_name_for')`` returns ``'User name for'``.
    """
    name       = name.replace( '_', ' ' ).capitalize()
    result     = ''
    last_lower = 0
    for c in name:
        if (c in uppercase) and last_lower:
           result += ' '
        last_lower = (c in lowercase)
        result    += c
    return result

#-------------------------------------------------------------------------------
#  Gets the path to the traits home directory:
#-------------------------------------------------------------------------------

_traits_home = None

def traits_home ( ):
    """ Gets the path to the Traits home directory.
    """
    global _traits_home

    if _traits_home is None:
        _traits_home = _verify_path( join( ETSConfig.application_data, 'traits' ) )

    return _traits_home

#-------------------------------------------------------------------------------
#  Verify that a specified path exists, and try to create it if it doesn't:
#-------------------------------------------------------------------------------

def _verify_path ( path ):
    """ Verify that a specified path exists, and try to create it if it
        does not exist.
    """
    if not exists( path ):
        try:
            os.mkdir( path )
        except:
            pass
    return path

#-------------------------------------------------------------------------------
#  Returns the name of the module the caller's caller is located in:
#-------------------------------------------------------------------------------

def get_module_name ( level = 2 ):
    return sys._getframe( level ).f_globals.get( '__name__' )


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