Added casting versions of all the basic traitlet types.

IPython/utils/traitlets.py

@@ -1,752 +1,828
 #!/usr/bin/env python
 # encoding: utf-8
 """
 A lightweight Traits like module.
 
 This is designed to provide a lightweight, simple, pure Python version of
 many of the capabilities of enthought.traits.  This includes:
 
 * Validation
 * Type specification with defaults
 * Static and dynamic notification
 * Basic predefined types
 * An API that is similar to enthought.traits
 
 We don't support:
 
 * Delegation
 * Automatic GUI generation
 * A full set of trait types
 * API compatibility with enthought.traits
 
 We choose to create this module because we need these capabilities, but
 we need them to be pure Python so they work in all Python implementations,
 including Jython and IronPython.
 
 Authors:
 
 * Brian Granger
 * Enthought, Inc.  Some of the code in this file comes from enthought.traits
   and is licensed under the BSD license.  Also, many of the ideas also come
   from enthought.traits even though our implementation is very different.
 """
 
 #-----------------------------------------------------------------------------
 #  Copyright (C) 2008-2009  The IPython Development Team
 #
 #  Distributed under the terms of the BSD License.  The full license is in
 #  the file COPYING, distributed as part of this software.
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # Imports
 #-----------------------------------------------------------------------------
 
 
 import inspect
 import sys
 import types
 from types import InstanceType, ClassType
 
 ClassTypes = (ClassType, type)
 
 #-----------------------------------------------------------------------------
 # Basic classes
 #-----------------------------------------------------------------------------
 
 
 class NoDefaultSpecified ( object ): pass
 NoDefaultSpecified = NoDefaultSpecified()
 
 
 class Undefined ( object ): pass
 Undefined = Undefined()
 
 
 class TraitletError(Exception):
     pass
 
 
 #-----------------------------------------------------------------------------
 # Utilities
 #-----------------------------------------------------------------------------
 
 
 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__ )
 
 
 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
 
 
 def repr_type(obj):
     """ Return a string representation of a value and its type for readable
     error messages.
     """
     the_type = type(obj)
     if the_type is InstanceType:
         # Old-style class.
         the_type = obj.__class__
     msg = '%r %r' % (obj, the_type)
     return msg
 
 
 def parse_notifier_name(name):
     """Convert the name argument to a list of names.
     
     Examples
     --------
     
     >>> parse_notifier_name('a')
     ['a']
     >>> parse_notifier_name(['a','b'])
     ['a', 'b']
     >>> parse_notifier_name(None)
     ['anytraitlet']
     """
     if isinstance(name, str):
         return [name]
     elif name is None:
         return ['anytraitlet']
     elif isinstance(name, (list, tuple)):
         for n in name:
             assert isinstance(n, str), "names must be strings"
         return name
 
 
 def get_module_name ( level = 2 ):
     """ Returns the name of the module that the caller's caller is located in.
     """
     return sys._getframe( level ).f_globals.get( '__name__', '__main__' )
 
 
 #-----------------------------------------------------------------------------
 # Base TraitletType for all traitlets
 #-----------------------------------------------------------------------------
 
 
 class TraitletType(object):
 
     metadata = {}
     default_value = Undefined
     info_text = 'any value'
 
     def __init__(self, default_value=NoDefaultSpecified, **metadata):
         """Create a TraitletType.
         """
         if default_value is not NoDefaultSpecified:
             self.default_value = default_value
         self.metadata.update(metadata)
         self.init()
 
     def init(self):
         pass
 
     def get_default_value(self):
         """Create a new instance of the default value."""
         dv = self.default_value
         return dv
 
     def __get__(self, obj, cls=None):
         """Get the value of the traitlet by self.name for the instance.
         
         The creation of default values is deferred until this is called the
         first time.  This is done so instances of the parent HasTraitlets
         will have their own default value instances.
         """
         if obj is None:
             return self
         else:
             if not obj._traitlet_values.has_key(self.name):
                 dv = self.get_default_value()
                 self.__set__(obj, dv, first=True)
                 return dv
             else:
                 return obj._traitlet_values[self.name]
 
     def __set__(self, obj, value, first=False):
         new_value = self._validate(obj, value)
         if not first:
             old_value = self.__get__(obj)
             if old_value != new_value:
                 obj._traitlet_values[self.name] = new_value
                 obj._notify(self.name, old_value, new_value)
         else:
             obj._traitlet_values[self.name] = new_value
 
     def _validate(self, obj, value):
         if hasattr(self, 'validate'):
             return self.validate(obj, value)
         elif hasattr(self, 'is_valid_for'):
             valid = self.is_valid_for(value)
             if valid:
                 return value
             else:
                 raise TraitletError('invalid value for type: %r' % value)
         elif hasattr(self, 'value_for'):
             return self.value_for(value)
         else:
             return value
 
     def info(self):
         return self.info_text
 
     def error(self, obj, value):
         if obj is not None:
             e = "The '%s' traitlet of %s instance must be %s, but a value of %s was specified." \
                 % (self.name, class_of(obj),
                    self.info(), repr_type(value))
         else:
             e = "The '%s' traitlet must be %s, but a value of %r was specified." \
                 % (self.name, self.info(), repr_type(value))            
         raise TraitletError(e)
 
 
 #-----------------------------------------------------------------------------
 # The HasTraitlets implementation
 #-----------------------------------------------------------------------------
 
 
 class MetaHasTraitlets(type):
     """A metaclass for HasTraitlets.
     
     This metaclass makes sure that any TraitletType class attributes are
     instantiated and sets their name attribute.
     """
     
     def __new__(mcls, name, bases, classdict):
         for k,v in classdict.iteritems():
             if isinstance(v, TraitletType):
                 v.name = k
             elif inspect.isclass(v):
                 if issubclass(v, TraitletType):
                     vinst = v()
                     vinst.name = k
                     classdict[k] = vinst
         return super(MetaHasTraitlets, mcls).__new__(mcls, name, bases, classdict)
 
 
 class HasTraitlets(object):
 
     __metaclass__ = MetaHasTraitlets
 
     def __init__(self):
         self._traitlet_values = {}
         self._traitlet_notifiers = {}
 
     def _notify(self, name, old_value, new_value):
 
         # First dynamic ones
         callables = self._traitlet_notifiers.get(name,[])
         more_callables = self._traitlet_notifiers.get('anytraitlet',[])
         callables.extend(more_callables)
 
         # Now static ones
         try:
             cb = getattr(self, '_%s_changed' % name)
         except:
             pass
         else:
             callables.append(cb)
 
         # Call them all now
         for c in callables:
             # Traits catches and logs errors here.  I allow them to raise
             if callable(c):
                 argspec = inspect.getargspec(c)
                 nargs = len(argspec[0])
                 # Bound methods have an additional 'self' argument
                 # I don't know how to treat unbound methods, but they
                 # can't really be used for callbacks.
                 if isinstance(c, types.MethodType):
                     offset = -1
                 else:
                     offset = 0
                 if nargs + offset == 0:
                     c()
                 elif nargs + offset == 1:
                     c(name)
                 elif nargs + offset == 2:
                     c(name, new_value)
                 elif nargs + offset == 3:
                     c(name, old_value, new_value)
                 else:
                     raise TraitletError('a traitlet changed callback '
                                         'must have 0-3 arguments.')
             else:
                 raise TraitletError('a traitlet changed callback '
                                     'must be callable.')
                 
 
     def _add_notifiers(self, handler, name):
         if not self._traitlet_notifiers.has_key(name):
             nlist = []
             self._traitlet_notifiers[name] = nlist
         else:
             nlist = self._traitlet_notifiers[name]
         if handler not in nlist:
             nlist.append(handler)
 
     def _remove_notifiers(self, handler, name):
         if self._traitlet_notifiers.has_key(name):
             nlist = self._traitlet_notifiers[name]
             try:
                 index = nlist.index(handler)
             except ValueError:
                 pass
             else:
                 del nlist[index]
 
     def on_traitlet_change(self, handler, name=None, remove=False):
         """Setup a handler to be called when a traitlet changes.
 
         This is used to setup dynamic notifications of traitlet changes.
         
         Static handlers can be created by creating methods on a HasTraitlets
         subclass with the naming convention '_[traitletname]_changed'.  Thus,
         to create static handler for the traitlet 'a', create the method
         _a_changed(self, name, old, new) (fewer arguments can be used, see
         below).
         
         Parameters
         ----------
             handler : callable
                 A callable that is called when a traitlet changes.  Its 
                 signature can be handler(), handler(name), handler(name, new)
                 or handler(name, old, new).
             name : list, str, None
                 If None, the handler will apply to all traitlets.  If a list
                 of str, handler will apply to all names in the list.  If a
                 str, the handler will apply just to that name.
             remove : bool
                 If False (the default), then install the handler.  If True
                 then unintall it.
         """
         if remove:
             names = parse_notifier_name(name)
             for n in names:
                 self._remove_notifiers(handler, n)
         else:
             names = parse_notifier_name(name)
             for n in names:
                 self._add_notifiers(handler, n)
 
     def _add_class_traitlet(self, name, traitlet):
         """Add a class-level traitlet.
 
         This create a new traitlet attached to all instances of this class.
         But, the value can be different on each instance.  But, this behavior
         is likely to trip up many folks as they would expect the traitlet
         type to be different on each instance.
 
         Parameters
         ----------
         name : str
             The name of the traitlet.
         traitlet : TraitletType or an instance of one
             The traitlet to assign to the name.
         """
         if inspect.isclass(traitlet):
             inst = traitlet()
         else:
             inst = traitlet
         assert isinstance(inst, TraitletType)
         inst.name = name
         setattr(self.__class__, name, inst)
 
 
 #-----------------------------------------------------------------------------
 # Actual TraitletTypes implementations/subclasses
 #-----------------------------------------------------------------------------
 
 #-----------------------------------------------------------------------------
 # TraitletTypes subclasses for handling classes and instances of classes
 #-----------------------------------------------------------------------------
 
 
 class BaseClassResolver(TraitletType):
     """Mixin class for traitlets that need to resolve classes by strings.
     
     This class provides is a mixin that provides its subclasses with the 
     ability to resolve classes by specifying a string name (for example,
     'foo.bar.MyClass').  An actual class can also be resolved.
 
     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')).
     """
 
     def resolve_class(self, obj, value):
         klass = self.validate_class(self.find_class(self.klass))
         if klass is None:
             self.validate_failed(obj, 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, obj, value):
         kind = type(value)
         if kind is InstanceType:
             msg = 'class %s' % value.__class__.__name__
         else:
             msg = '%s (i.e. %s)' % ( str( kind )[1:-1], repr( value ) )
 
         self.error(obj, msg)
 
 
 class Type(BaseClassResolver):
     """A traitlet whose value must be a subclass of a specified class."""
 
     def __init__ (self, default_value=None, klass=None, allow_none=True, **metadata ):
         """Construct a Type traitlet
 
         A Type traitlet specifies that its values must be subclasses of
         a particular class.
 
         Parameters
         ----------
         default_value : class or None
             The default value must be a subclass of klass.
         klass : class, str, None
             Values of this traitlet must be a subclass of klass.  The klass
             may be specified in a string like: 'foo.bar.MyClass'.
         allow_none : boolean
             Indicates whether None is allowed as an assignable value. Even if
             ``False``, the default value may be ``None``.
         """
         if default_value is None:
             if klass is None:
                 klass = object
         elif klass is None:
             klass = default_value
 
         if isinstance(klass, basestring):
             self.validate = self.resolve
         elif not isinstance(klass, ClassTypes):
             raise TraitletError("A Type traitlet must specify a class.")
 
         self.klass       = klass
         self._allow_none = allow_none
         self.module      = get_module_name()
 
         super(Type, self).__init__(default_value, **metadata)
 
     def validate(self, obj, 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(obj, value)
 
     def resolve(self, obj, 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(obj, value)
             del self.validate
 
         return self.validate(obj, 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()
 
         dv = self.resolve_default_value()
         dvt = type(dv)
         return (dvt, dv)
 
     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)
                 del self.validate
             except:
                 raise TraitletError('Could not resolve %s into a valid class' %
                                     self.klass )
 
         return self.klass
 
 
 class DefaultValueGenerator(object):
     """A class for generating new default value instances."""
 
     def __init__(self, klass, *args, **kw):
         self.klass = klass
         self.args = args
         self.kw = kw
 
 
 class Instance(BaseClassResolver):
     """A trait whose value must be an instance of a specified class.
     
     The value can also be an instance of a subclass of the specified class.
     """
 
     def __init__(self, klass=None, args=None, kw=None, allow_none=True, 
                  module = None, **metadata ):
         """Construct an Instance traitlet.
 
         Parameters
         ----------
         klass : class or instance
             The object that forms the basis for the traitlet.  If an instance
             values must have isinstance(value, type(instance)).
         args : tuple
             Positional arguments for generating the default value.
         kw : dict
             Keyword arguments for generating the default value.
         allow_none : bool
             Indicates whether None is allowed as a value.
 
         Default Value
         -------------
         If klass is an instance, default value is None.  If klass is a class
         then the default value is obtained by calling ``klass(*args, **kw)``.
         If klass is a str, it is first resolved to an actual class and then
         instantiated with ``klass(*args, **kw)``.
         """
 
         self._allow_none = allow_none
         self.module      = module or get_module_name()
 
         if klass is None:
             raise TraitletError('A %s traitlet must have a class specified.' %
                                 self.__class__.__name__ )
         elif not isinstance(klass, (basestring,) + ClassTypes ):
             # klass is an instance so default value will be None
             self.klass = klass.__class__
             default_value = None
         else:
             # klass is a str or class so we handle args, kw
             if args is None:
                 args = ()
             if kw is None:
                 if isinstance(args, dict):
                     kw = args
                     args = ()
                 else:
                     kw = {}
             if not isinstance(kw, dict):
                 raise TraitletError("The 'kw' argument must be a dict.")
             if not isinstance(args, tuple):
                 raise TraitletError("The 'args' argument must be a tuple.")
             self.klass = klass
             # This tells my get_default_value that the default value
             # instance needs to be generated when it is called.  This 
             # is usually when TraitletType.__get__ is called for the 1st time.
             
             default_value = DefaultValueGenerator(klass, *args, **kw)
 
         super(Instance, self).__init__(default_value, **metadata)
 
     def validate(self, obj, value):
         if value is None:
             if self._allow_none:
                 return value
             self.validate_failed(obj, value)
 
         # This is where self.klass is turned into a real class if it was
         # a str initially.  This happens the first time TraitletType.__set__
         # is called.  This does happen if a default value is generated by
         # TraitletType.__get__.
         if isinstance(self.klass, basestring):
             self.resolve_class(obj, value)
 
         if isinstance(value, self.klass):
             return value
         else:
             self.validate_failed(obj, value)
 
     def info ( self ):
         klass = self.klass
         if not isinstance( klass, basestring ):
             klass = klass.__name__
         result = class_of(klass)
         if self._allow_none:
             return result + ' or None'
 
         return result
 
     def get_default_value ( self ):
         """Instantiate a default value instance.
         
         When TraitletType.__get__ is called the first time, this is called
         (if no value has been assigned) to get a default value instance.
         """
         dv  = self.default_value
         if isinstance(dv, DefaultValueGenerator):
             klass = dv.klass
             args = dv.args
             kw = dv.kw
             if isinstance(klass, basestring):
                 klass = self.validate_class(self.find_class(klass))
                 if klass is None:
                     raise TraitletError('Unable to locate class: ' + dv.klass)
             return klass(*args, **kw)
         else:
             return dv
 
 
 #-----------------------------------------------------------------------------
 # Basic TraitletTypes implementations/subclasses
 #-----------------------------------------------------------------------------
 
 
 class Any(TraitletType):
     default_value = None
     info_text = 'any value'
 
 
 class Int(TraitletType):
+    """A integer traitlet."""
 
     evaluate = int
     default_value = 0
     info_text = 'an integer'
 
     def validate(self, obj, value):
         if isinstance(value, int):
             return value
         self.error(obj, value)
 
+class CInt(Int):
+    """A casting version of the int traitlet."""
+
+    def validate(self, obj, value):
+        try:
+            return int(value)
+        except:
+            self.error(obj, value)
+
 
 class Long(TraitletType):
+    """A long integer traitlet."""
 
     evaluate = long
     default_value = 0L
     info_text = 'a long'
 
     def validate(self, obj, value):
         if isinstance(value, long):
             return value
         if isinstance(value, int):
             return long(value)
         self.error(obj, value)
 
 
+class CLong(Long):
+    """A casting version of the long integer traitlet."""
+
+    def validate(self, obj, value):
+        try:
+            return long(value)
+        except:
+            self.error(obj, value)
+
+
 class Float(TraitletType):
+    """A float traitlet."""
 
     evaluate = float
     default_value = 0.0
     info_text = 'a float'
 
     def validate(self, obj, value):
         if isinstance(value, float):
             return value
         if isinstance(value, int):
             return float(value)
         self.error(obj, value)
 
 
+class CFloat(Float):
+    """A casting version of the float traitlet."""
+
+    def validate(self, obj, value):
+        try:
+            return float(value)
+        except:
+            self.error(obj, value)
+
 class Complex(TraitletType):
+    """A traitlet for complex numbers."""
 
     evaluate = complex
     default_value = 0.0 + 0.0j
     info_text = 'a complex number'
 
     def validate(self, obj, value):
         if isinstance(value, complex):
             return value
         if isinstance(value, (float, int)):
             return complex(value)
         self.error(obj, value)
 
 
+class CComplex(Complex):
+    """A casting version of the complex number traitlet."""
+
+    def validate (self, obj, value):
+        try:
+            return complex(value)
+        except:
+            self.error(obj, value)
+
+
 class Str(TraitletType):
+    """A traitlet for strings."""
 
     evaluate = lambda x: x
     default_value = ''
     info_text = 'a string'
 
     def validate(self, obj, value):
         if isinstance(value, str):
             return value
         self.error(obj, value)
 
 
+class CStr(Str):
+    """A casting version of the string traitlet."""
+
+    def validate(self, obj, value):
+        try:
+            return str(value)
+        except:
+            try:
+                return unicode(value)
+            except:
+                self.error(obj, value)
+
+
 class Unicode(TraitletType):
+    """A traitlet for unicode strings."""
 
     evaluate = unicode
     default_value = u''
     info_text = 'a unicode string'
 
     def validate(self, obj, value):
         if isinstance(value, unicode):
             return value
         if isinstance(value, str):
             return unicode(value)
         self.error(obj, value)
 
 
-class Bool(TraitletType):
+class CUnicode(Unicode):
+    """A casting version of the unicode traitlet."""
 
+    def validate(self, obj, value):
+        try:
+            return unicode(value)
+        except:
+            self.error(obj, value)
+
+
+class Bool(TraitletType):
+    """A boolean (True, False) traitlet."""
     evaluate = bool
     default_value = False
     info_text = 'a boolean'
 
     def validate(self, obj, value):
         if isinstance(value, bool):
             return value
         self.error(obj, value)
 
+
+class CBool(Bool):
+    """A casting version of the boolean traitlet."""
+
+    def validate(self, obj, value):
+        try:
+            return bool(value)
+        except:
+            self.error(obj, value)
  No newline at end of file