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Diffstat (limited to 'lib/python2.7/abc.py')
| -rw-r--r-- | lib/python2.7/abc.py | 185 |
1 files changed, 185 insertions, 0 deletions
diff --git a/lib/python2.7/abc.py b/lib/python2.7/abc.py new file mode 100644 index 0000000..02e48a1 --- /dev/null +++ b/lib/python2.7/abc.py @@ -0,0 +1,185 @@ +# Copyright 2007 Google, Inc. All Rights Reserved. +# Licensed to PSF under a Contributor Agreement. + +"""Abstract Base Classes (ABCs) according to PEP 3119.""" + +import types + +from _weakrefset import WeakSet + +# Instance of old-style class +class _C: pass +_InstanceType = type(_C()) + + +def abstractmethod(funcobj): + """A decorator indicating abstract methods. + + Requires that the metaclass is ABCMeta or derived from it. A + class that has a metaclass derived from ABCMeta cannot be + instantiated unless all of its abstract methods are overridden. + The abstract methods can be called using any of the normal + 'super' call mechanisms. + + Usage: + + class C: + __metaclass__ = ABCMeta + @abstractmethod + def my_abstract_method(self, ...): + ... + """ + funcobj.__isabstractmethod__ = True + return funcobj + + +class abstractproperty(property): + """A decorator indicating abstract properties. + + Requires that the metaclass is ABCMeta or derived from it. A + class that has a metaclass derived from ABCMeta cannot be + instantiated unless all of its abstract properties are overridden. + The abstract properties can be called using any of the normal + 'super' call mechanisms. + + Usage: + + class C: + __metaclass__ = ABCMeta + @abstractproperty + def my_abstract_property(self): + ... + + This defines a read-only property; you can also define a read-write + abstract property using the 'long' form of property declaration: + + class C: + __metaclass__ = ABCMeta + def getx(self): ... + def setx(self, value): ... + x = abstractproperty(getx, setx) + """ + __isabstractmethod__ = True + + +class ABCMeta(type): + + """Metaclass for defining Abstract Base Classes (ABCs). + + Use this metaclass to create an ABC. An ABC can be subclassed + directly, and then acts as a mix-in class. You can also register + unrelated concrete classes (even built-in classes) and unrelated + ABCs as 'virtual subclasses' -- these and their descendants will + be considered subclasses of the registering ABC by the built-in + issubclass() function, but the registering ABC won't show up in + their MRO (Method Resolution Order) nor will method + implementations defined by the registering ABC be callable (not + even via super()). + + """ + + # A global counter that is incremented each time a class is + # registered as a virtual subclass of anything. It forces the + # negative cache to be cleared before its next use. + _abc_invalidation_counter = 0 + + def __new__(mcls, name, bases, namespace): + cls = super(ABCMeta, mcls).__new__(mcls, name, bases, namespace) + # Compute set of abstract method names + abstracts = set(name + for name, value in namespace.items() + if getattr(value, "__isabstractmethod__", False)) + for base in bases: + for name in getattr(base, "__abstractmethods__", set()): + value = getattr(cls, name, None) + if getattr(value, "__isabstractmethod__", False): + abstracts.add(name) + cls.__abstractmethods__ = frozenset(abstracts) + # Set up inheritance registry + cls._abc_registry = WeakSet() + cls._abc_cache = WeakSet() + cls._abc_negative_cache = WeakSet() + cls._abc_negative_cache_version = ABCMeta._abc_invalidation_counter + return cls + + def register(cls, subclass): + """Register a virtual subclass of an ABC.""" + if not isinstance(subclass, (type, types.ClassType)): + raise TypeError("Can only register classes") + if issubclass(subclass, cls): + return # Already a subclass + # Subtle: test for cycles *after* testing for "already a subclass"; + # this means we allow X.register(X) and interpret it as a no-op. + if issubclass(cls, subclass): + # This would create a cycle, which is bad for the algorithm below + raise RuntimeError("Refusing to create an inheritance cycle") + cls._abc_registry.add(subclass) + ABCMeta._abc_invalidation_counter += 1 # Invalidate negative cache + + def _dump_registry(cls, file=None): + """Debug helper to print the ABC registry.""" + print >> file, "Class: %s.%s" % (cls.__module__, cls.__name__) + print >> file, "Inv.counter: %s" % ABCMeta._abc_invalidation_counter + for name in sorted(cls.__dict__.keys()): + if name.startswith("_abc_"): + value = getattr(cls, name) + print >> file, "%s: %r" % (name, value) + + def __instancecheck__(cls, instance): + """Override for isinstance(instance, cls).""" + # Inline the cache checking when it's simple. + subclass = getattr(instance, '__class__', None) + if subclass is not None and subclass in cls._abc_cache: + return True + subtype = type(instance) + # Old-style instances + if subtype is _InstanceType: + subtype = subclass + if subtype is subclass or subclass is None: + if (cls._abc_negative_cache_version == + ABCMeta._abc_invalidation_counter and + subtype in cls._abc_negative_cache): + return False + # Fall back to the subclass check. + return cls.__subclasscheck__(subtype) + return (cls.__subclasscheck__(subclass) or + cls.__subclasscheck__(subtype)) + + def __subclasscheck__(cls, subclass): + """Override for issubclass(subclass, cls).""" + # Check cache + if subclass in cls._abc_cache: + return True + # Check negative cache; may have to invalidate + if cls._abc_negative_cache_version < ABCMeta._abc_invalidation_counter: + # Invalidate the negative cache + cls._abc_negative_cache = WeakSet() + cls._abc_negative_cache_version = ABCMeta._abc_invalidation_counter + elif subclass in cls._abc_negative_cache: + return False + # Check the subclass hook + ok = cls.__subclasshook__(subclass) + if ok is not NotImplemented: + assert isinstance(ok, bool) + if ok: + cls._abc_cache.add(subclass) + else: + cls._abc_negative_cache.add(subclass) + return ok + # Check if it's a direct subclass + if cls in getattr(subclass, '__mro__', ()): + cls._abc_cache.add(subclass) + return True + # Check if it's a subclass of a registered class (recursive) + for rcls in cls._abc_registry: + if issubclass(subclass, rcls): + cls._abc_cache.add(subclass) + return True + # Check if it's a subclass of a subclass (recursive) + for scls in cls.__subclasses__(): + if issubclass(subclass, scls): + cls._abc_cache.add(subclass) + return True + # No dice; update negative cache + cls._abc_negative_cache.add(subclass) + return False |