1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
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
|
