#!/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. Most importantly, we don't provide container traitlets (list, dict, tuple) that can trigger notifications if their contents change. * API compatibility with enthought.traits There are also some important difference in our design: * enthought.traits does not validate default values. We do. 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, FunctionType 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 class _SimpleTest: def __init__ ( self, value ): self.value = value def __call__ ( self, test ): print test, self.value return test == self.value def __repr__(self): return " 0: if len(self.metadata) > 0: self._metadata = self.metadata.copy() self._metadata.update(metadata) else: self._metadata = metadata else: self._metadata = self.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 set_default_value(self, obj): dv = self.get_default_value() newdv = self._validate(obj, dv) obj._traitlet_values[self.name] = newdv def __get__(self, obj, cls=None): """Get the value of the traitlet by self.name for the instance. Default values are instantiated when :meth:`HasTraitlets.__new__` is called. Thus by the time this method gets called either the default value or a user defined value (they called :meth:`__set__`) is in the :class:`HasTraitlets` instance. """ if obj is None: return self else: try: value = obj._traitlet_values[self.name] except: # HasTraitlets should call set_default_value to populate # this. So this should never be reached. raise TraitletError('Unexpected error in TraitletType: ' 'default value not set properly') else: return value def __set__(self, obj, value): new_value = self._validate(obj, value) old_value = self.__get__(obj) if old_value != new_value: obj._traitlet_values[self.name] = new_value obj._notify_traitlet(self.name, old_value, 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) def get_metadata(self, key): return getattr(self, '_metadata', {}).get(key, None) def set_metadata(self, key, value): getattr(self, '_metadata', {})[key] = value #----------------------------------------------------------------------------- # 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): """Create the HasTraitlets class. This instantiates all TraitletTypes in the class dict and sets their :attr:`name` attribute. """ # print "=========================" # print "MetaHasTraitlets.__new__" # print "mcls, ", mcls # print "name, ", name # print "bases, ", bases # print "classdict, ", 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) def __init__(cls, name, bases, classdict): """Finish initializing the HasTraitlets class. This sets the :attr:`this_class` attribute of each TraitletType in the class dict to the newly created class ``cls``. """ # print "=========================" # print "MetaHasTraitlets.__init__" # print "cls, ", cls # print "name, ", name # print "bases, ", bases # print "classdict, ", classdict for k, v in classdict.iteritems(): if isinstance(v, TraitletType): v.this_class = cls super(MetaHasTraitlets, cls).__init__(name, bases, classdict) class HasTraitlets(object): __metaclass__ = MetaHasTraitlets def __new__(cls, *args, **kw): inst = super(HasTraitlets, cls).__new__(cls, *args, **kw) inst._traitlet_values = {} inst._traitlet_notifiers = {} # Here we tell all the TraitletType instances to set their default # values on the instance. for key in dir(cls): value = getattr(cls, key) if isinstance(value, TraitletType): value.set_default_value(inst) return inst # def __init__(self): # self._traitlet_values = {} # self._traitlet_notifiers = {} def _notify_traitlet(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 traitlet_names(self, **metadata): """Get a list of all the names of this classes traitlets.""" return self.traitlets(**metadata).keys() def traitlets(self, **metadata): """Get a list of all the traitlets of this class. The TraitletTypes returned don't know anything about the values that the various HasTraitlet's instances are holding. """ traitlets = dict([memb for memb in inspect.getmembers(self.__class__) if \ isinstance(memb[1], TraitletType)]) if len(metadata) == 0: return traitlets for meta_name, meta_eval in metadata.items(): if type(meta_eval) is not FunctionType: metadata[meta_name] = _SimpleTest(meta_eval) result = {} for name, traitlet in traitlets.items(): for meta_name, meta_eval in metadata.items(): if not meta_eval(traitlet.get_metadata(meta_name)): break else: result[name] = traitlet return result def traitlet_metadata(self, traitletname, key): """Get metadata values for traitlet by key.""" try: traitlet = getattr(self.__class__, traitletname) except AttributeError: raise TraitletError("Class %s does not have a traitlet named %s" % (self.__class__.__name__, traitletname)) else: return traitlet.get_metadata(key) #----------------------------------------------------------------------------- # Actual TraitletTypes implementations/subclasses #----------------------------------------------------------------------------- #----------------------------------------------------------------------------- # TraitletTypes subclasses for handling classes and instances of classes #----------------------------------------------------------------------------- class ClassBasedTraitletType(TraitletType): """A traitlet with error reporting for Type, Instance and This.""" def error(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 ) ) super(ClassBasedTraitletType, self).error(obj, msg) class Type(ClassBasedTraitletType): """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 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 not inspect.isclass(klass): raise TraitletError("A Type traitlet must specify a class.") self.klass = klass self._allow_none = allow_none 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 info(self): """ Returns a description of the trait.""" klass = self.klass.__name__ result = 'a subclass of ' + klass if self._allow_none: return result + ' or None' return result 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 def generate(self): return self.klass(*self.args, **self.kw) class Instance(ClassBasedTraitletType): """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, **metadata ): """Construct an Instance traitlet. This traitlet allows values that are instances of a particular class or its sublclasses. Our implementation is quite different from that of enthough.traits as we don't allow instances to be used for klass and we handle the ``args`` and ``kw`` arguments differently. Parameters ---------- klass : class The class that forms the basis for the traitlet. Instances and strings are not allowed. 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 both ``args`` and ``kw`` are None, then the default value is None. If ``args`` is a tuple and ``kw`` is a dict, then the default is created as ``klass(*args, **kw)``. If either ``args`` or ``kw`` is not (but not both), None is replace by ``()`` or ``{}``. """ self._allow_none = allow_none if (klass is None) or (not inspect.isclass(klass)): raise TraitletError('The klass argument must be a class' ' you gave: %r' % klass) self.klass = klass # self.klass is a class, so handle default_value if args is None and kw is None: default_value = None else: if args is None: # kw is not None args = () elif kw is None: # args is not None kw = {} if not isinstance(kw, dict): raise TraitletError("The 'kw' argument must be a dict or None.") if not isinstance(args, tuple): raise TraitletError("The 'args' argument must be a tuple or None.") default_value = DefaultValueGenerator(self.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.error(obj, value) if isinstance(value, self.klass): return value else: self.error(obj, value) def info(self): klass = self.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. This is called when the containing HasTraitlets classes' :meth:`__new__` method is called to ensure that a unique instance is created for each HasTraitlets instance. """ dv = self.default_value if isinstance(dv, DefaultValueGenerator): return dv.generate() else: return dv class This(ClassBasedTraitletType): """A traitlet for instances of the class containing this trait. Because how how and when class bodies are executed, the ``This`` traitlet can only have a default value of None. This, and because we always validate default values, ``allow_none`` is *always* true. """ info_text = 'an instance of the same type as the receiver or None' def __init__(self, **metadata): super(This, self).__init__(None, **metadata) def validate(self, obj, value): # What if value is a superclass of obj.__class__? This is # complicated if it was the superclass that defined the This # traitlet. if isinstance(value, self.this_class) or (value is None): return value else: self.error(obj, value) #----------------------------------------------------------------------------- # 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 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)