Mercurial > cpython-lru_cache-weakref

annotate Lib/abc.py @ 80661:94de77bd0b4b 2.7

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Issue #16194: document imp.load_dynamic problems when read several extension modules from the same binary object file.
author Andrew Svetlov <andrew.svetlov@gmail.com>
date Thu, 29 Nov 2012 19:51:28 +0200
parents b36cb4602e21
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 # Copyright 2007 Google, Inc. All Rights Reserved.
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2 # Licensed to PSF under a Contributor Agreement.
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3
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4 """Abstract Base Classes (ABCs) according to PEP 3119."""
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5
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6 import types
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7
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8 from _weakrefset import WeakSet
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9
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10 # Instance of old-style class
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11 class _C: pass
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12 _InstanceType = type(_C())
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13
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14
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15 def abstractmethod(funcobj):
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16 """A decorator indicating abstract methods.
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17
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18 Requires that the metaclass is ABCMeta or derived from it. A
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19 class that has a metaclass derived from ABCMeta cannot be
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20 instantiated unless all of its abstract methods are overridden.
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21 The abstract methods can be called using any of the normal
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22 'super' call mechanisms.
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23
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24 Usage:
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25
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26 class C:
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27 __metaclass__ = ABCMeta
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28 @abstractmethod
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29 def my_abstract_method(self, ...):
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30 ...
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31 """
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32 funcobj.__isabstractmethod__ = True
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33 return funcobj
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34
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35
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36 class abstractproperty(property):
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37 """A decorator indicating abstract properties.
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38
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39 Requires that the metaclass is ABCMeta or derived from it. A
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40 class that has a metaclass derived from ABCMeta cannot be
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41 instantiated unless all of its abstract properties are overridden.
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42 The abstract properties can be called using any of the normal
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43 'super' call mechanisms.
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44
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45 Usage:
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46
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47 class C:
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48 __metaclass__ = ABCMeta
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49 @abstractproperty
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50 def my_abstract_property(self):
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51 ...
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52
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53 This defines a read-only property; you can also define a read-write
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54 abstract property using the 'long' form of property declaration:
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55
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56 class C:
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57 __metaclass__ = ABCMeta
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58 def getx(self): ...
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59 def setx(self, value): ...
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60 x = abstractproperty(getx, setx)
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61 """
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62 __isabstractmethod__ = True
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63
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64
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65 class ABCMeta(type):
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66
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67 """Metaclass for defining Abstract Base Classes (ABCs).
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68
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69 Use this metaclass to create an ABC. An ABC can be subclassed
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70 directly, and then acts as a mix-in class. You can also register
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71 unrelated concrete classes (even built-in classes) and unrelated
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72 ABCs as 'virtual subclasses' -- these and their descendants will
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73 be considered subclasses of the registering ABC by the built-in
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74 issubclass() function, but the registering ABC won't show up in
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75 their MRO (Method Resolution Order) nor will method
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76 implementations defined by the registering ABC be callable (not
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77 even via super()).
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78
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79 """
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80
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81 # A global counter that is incremented each time a class is
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82 # registered as a virtual subclass of anything. It forces the
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83 # negative cache to be cleared before its next use.
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84 _abc_invalidation_counter = 0
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85
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86 def __new__(mcls, name, bases, namespace):
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87 cls = super(ABCMeta, mcls).__new__(mcls, name, bases, namespace)
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88 # Compute set of abstract method names
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89 abstracts = set(name
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90 for name, value in namespace.items()
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91 if getattr(value, "__isabstractmethod__", False))
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92 for base in bases:
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93 for name in getattr(base, "__abstractmethods__", set()):
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94 value = getattr(cls, name, None)
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95 if getattr(value, "__isabstractmethod__", False):
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96 abstracts.add(name)
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97 cls.__abstractmethods__ = frozenset(abstracts)
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98 # Set up inheritance registry
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99 cls._abc_registry = WeakSet()
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100 cls._abc_cache = WeakSet()
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101 cls._abc_negative_cache = WeakSet()
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102 cls._abc_negative_cache_version = ABCMeta._abc_invalidation_counter
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103 return cls
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104
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105 def register(cls, subclass):
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106 """Register a virtual subclass of an ABC."""
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107 if not isinstance(subclass, (type, types.ClassType)):
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108 raise TypeError("Can only register classes")
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109 if issubclass(subclass, cls):
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110 return # Already a subclass
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111 # Subtle: test for cycles *after* testing for "already a subclass";
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112 # this means we allow X.register(X) and interpret it as a no-op.
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113 if issubclass(cls, subclass):
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114 # This would create a cycle, which is bad for the algorithm below
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115 raise RuntimeError("Refusing to create an inheritance cycle")
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116 cls._abc_registry.add(subclass)
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117 ABCMeta._abc_invalidation_counter += 1 # Invalidate negative cache
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118
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119 def _dump_registry(cls, file=None):
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120 """Debug helper to print the ABC registry."""
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121 print >> file, "Class: %s.%s" % (cls.__module__, cls.__name__)
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122 print >> file, "Inv.counter: %s" % ABCMeta._abc_invalidation_counter
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123 for name in sorted(cls.__dict__.keys()):
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124 if name.startswith("_abc_"):
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125 value = getattr(cls, name)
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126 print >> file, "%s: %r" % (name, value)
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127
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128 def __instancecheck__(cls, instance):
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129 """Override for isinstance(instance, cls)."""
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130 # Inline the cache checking when it's simple.
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131 subclass = getattr(instance, '__class__', None)
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132 if subclass is not None and subclass in cls._abc_cache:
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133 return True
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134 subtype = type(instance)
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135 # Old-style instances
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136 if subtype is _InstanceType:
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137 subtype = subclass
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138 if subtype is subclass or subclass is None:
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139 if (cls._abc_negative_cache_version ==
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140 ABCMeta._abc_invalidation_counter and
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141 subtype in cls._abc_negative_cache):
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142 return False
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143 # Fall back to the subclass check.
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144 return cls.__subclasscheck__(subtype)
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145 return (cls.__subclasscheck__(subclass) or
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146 cls.__subclasscheck__(subtype))
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147
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148 def __subclasscheck__(cls, subclass):
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149 """Override for issubclass(subclass, cls)."""
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150 # Check cache
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151 if subclass in cls._abc_cache:
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152 return True
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153 # Check negative cache; may have to invalidate
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154 if cls._abc_negative_cache_version < ABCMeta._abc_invalidation_counter:
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155 # Invalidate the negative cache
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156 cls._abc_negative_cache = WeakSet()
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157 cls._abc_negative_cache_version = ABCMeta._abc_invalidation_counter
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158 elif subclass in cls._abc_negative_cache:
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159 return False
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160 # Check the subclass hook
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161 ok = cls.__subclasshook__(subclass)
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162 if ok is not NotImplemented:
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163 assert isinstance(ok, bool)
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164 if ok:
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165 cls._abc_cache.add(subclass)
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166 else:
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167 cls._abc_negative_cache.add(subclass)
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168 return ok
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169 # Check if it's a direct subclass
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170 if cls in getattr(subclass, '__mro__', ()):
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171 cls._abc_cache.add(subclass)
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172 return True
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173 # Check if it's a subclass of a registered class (recursive)
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174 for rcls in cls._abc_registry:
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175 if issubclass(subclass, rcls):
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176 cls._abc_cache.add(subclass)
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177 return True
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178 # Check if it's a subclass of a subclass (recursive)
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179 for scls in cls.__subclasses__():
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180 if issubclass(subclass, scls):
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181 cls._abc_cache.add(subclass)
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182 return True
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183 # No dice; update negative cache
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184 cls._abc_negative_cache.add(subclass)
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185 return False