Mercurial > cpython-lru_cache-weakref

annotate Lib/abc.py @ 79691:05c8928362ee

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Merge __next__ method link fixes with 3.3.
author Ezio Melotti <ezio.melotti@gmail.com>
date Fri, 12 Oct 2012 13:46:37 +0300
parents e979b26a9172
children 9347869d1066
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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 from _weakrefset import WeakSet
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7
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8 def abstractmethod(funcobj):
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9 """A decorator indicating abstract methods.
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10
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11 Requires that the metaclass is ABCMeta or derived from it. A
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12 class that has a metaclass derived from ABCMeta cannot be
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13 instantiated unless all of its abstract methods are overridden.
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14 The abstract methods can be called using any of the normal
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15 'super' call mechanisms.
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16
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17 Usage:
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18
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19 class C(metaclass=ABCMeta):
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20 @abstractmethod
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21 def my_abstract_method(self, ...):
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22 ...
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23 """
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24 funcobj.__isabstractmethod__ = True
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25 return funcobj
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26
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27
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28 class abstractclassmethod(classmethod):
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29 """
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30 A decorator indicating abstract classmethods.
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31
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32 Similar to abstractmethod.
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33
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34 Usage:
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35
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36 class C(metaclass=ABCMeta):
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37 @abstractclassmethod
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38 def my_abstract_classmethod(cls, ...):
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39 ...
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40
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41 'abstractclassmethod' is deprecated. Use 'classmethod' with
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42 'abstractmethod' instead.
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43 """
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44
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45 __isabstractmethod__ = True
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46
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47 def __init__(self, callable):
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48 callable.__isabstractmethod__ = True
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49 super().__init__(callable)
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50
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51
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52 class abstractstaticmethod(staticmethod):
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53 """
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54 A decorator indicating abstract staticmethods.
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55
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56 Similar to abstractmethod.
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57
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58 Usage:
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59
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60 class C(metaclass=ABCMeta):
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61 @abstractstaticmethod
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62 def my_abstract_staticmethod(...):
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63 ...
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64
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65 'abstractstaticmethod' is deprecated. Use 'staticmethod' with
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66 'abstractmethod' instead.
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67 """
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68
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69 __isabstractmethod__ = True
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70
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71 def __init__(self, callable):
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72 callable.__isabstractmethod__ = True
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73 super().__init__(callable)
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74
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75
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76 class abstractproperty(property):
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77 """
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78 A decorator indicating abstract properties.
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79
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80 Requires that the metaclass is ABCMeta or derived from it. A
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81 class that has a metaclass derived from ABCMeta cannot be
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82 instantiated unless all of its abstract properties are overridden.
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83 The abstract properties can be called using any of the normal
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84 'super' call mechanisms.
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85
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86 Usage:
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87
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88 class C(metaclass=ABCMeta):
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89 @abstractproperty
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90 def my_abstract_property(self):
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91 ...
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92
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93 This defines a read-only property; you can also define a read-write
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94 abstract property using the 'long' form of property declaration:
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95
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96 class C(metaclass=ABCMeta):
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97 def getx(self): ...
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98 def setx(self, value): ...
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99 x = abstractproperty(getx, setx)
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100
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101 'abstractproperty' is deprecated. Use 'property' with 'abstractmethod'
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102 instead.
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103 """
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104
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105 __isabstractmethod__ = True
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106
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107
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108 class ABCMeta(type):
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109
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110 """Metaclass for defining Abstract Base Classes (ABCs).
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111
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112 Use this metaclass to create an ABC. An ABC can be subclassed
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113 directly, and then acts as a mix-in class. You can also register
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114 unrelated concrete classes (even built-in classes) and unrelated
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115 ABCs as 'virtual subclasses' -- these and their descendants will
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116 be considered subclasses of the registering ABC by the built-in
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117 issubclass() function, but the registering ABC won't show up in
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118 their MRO (Method Resolution Order) nor will method
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119 implementations defined by the registering ABC be callable (not
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120 even via super()).
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121
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122 """
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123
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124 # A global counter that is incremented each time a class is
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125 # registered as a virtual subclass of anything. It forces the
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126 # negative cache to be cleared before its next use.
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127 _abc_invalidation_counter = 0
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128
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129 def __new__(mcls, name, bases, namespace):
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130 cls = super().__new__(mcls, name, bases, namespace)
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131 # Compute set of abstract method names
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132 abstracts = {name
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133 for name, value in namespace.items()
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134 if getattr(value, "__isabstractmethod__", False)}
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135 for base in bases:
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136 for name in getattr(base, "__abstractmethods__", set()):
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137 value = getattr(cls, name, None)
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138 if getattr(value, "__isabstractmethod__", False):
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139 abstracts.add(name)
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140 cls.__abstractmethods__ = frozenset(abstracts)
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141 # Set up inheritance registry
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142 cls._abc_registry = WeakSet()
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143 cls._abc_cache = WeakSet()
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144 cls._abc_negative_cache = WeakSet()
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145 cls._abc_negative_cache_version = ABCMeta._abc_invalidation_counter
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146 return cls
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147
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148 def register(cls, subclass):
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149 """Register a virtual subclass of an ABC.
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151 Returns the subclass, to allow usage as a class decorator.
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152 """
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153 if not isinstance(subclass, type):
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154 raise TypeError("Can only register classes")
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155 if issubclass(subclass, cls):
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156 return subclass # Already a subclass
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157 # Subtle: test for cycles *after* testing for "already a subclass";
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158 # this means we allow X.register(X) and interpret it as a no-op.
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159 if issubclass(cls, subclass):
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160 # This would create a cycle, which is bad for the algorithm below
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161 raise RuntimeError("Refusing to create an inheritance cycle")
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162 cls._abc_registry.add(subclass)
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163 ABCMeta._abc_invalidation_counter += 1 # Invalidate negative cache
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164 return subclass
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165
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166 def _dump_registry(cls, file=None):
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167 """Debug helper to print the ABC registry."""
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168 print("Class: %s.%s" % (cls.__module__, cls.__name__), file=file)
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169 print("Inv.counter: %s" % ABCMeta._abc_invalidation_counter, file=file)
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170 for name in sorted(cls.__dict__.keys()):
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171 if name.startswith("_abc_"):
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172 value = getattr(cls, name)
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173 print("%s: %r" % (name, value), file=file)
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174
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175 def __instancecheck__(cls, instance):
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176 """Override for isinstance(instance, cls)."""
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177 # Inline the cache checking
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178 subclass = instance.__class__
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179 if subclass in cls._abc_cache:
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180 return True
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181 subtype = type(instance)
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182 if subtype is subclass:
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183 if (cls._abc_negative_cache_version ==
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184 ABCMeta._abc_invalidation_counter and
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185 subclass in cls._abc_negative_cache):
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186 return False
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187 # Fall back to the subclass check.
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188 return cls.__subclasscheck__(subclass)
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189 return any(cls.__subclasscheck__(c) for c in {subclass, subtype})
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190
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191 def __subclasscheck__(cls, subclass):
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192 """Override for issubclass(subclass, cls)."""
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193 # Check cache
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194 if subclass in cls._abc_cache:
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195 return True
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196 # Check negative cache; may have to invalidate
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197 if cls._abc_negative_cache_version < ABCMeta._abc_invalidation_counter:
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198 # Invalidate the negative cache
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199 cls._abc_negative_cache = WeakSet()
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200 cls._abc_negative_cache_version = ABCMeta._abc_invalidation_counter
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201 elif subclass in cls._abc_negative_cache:
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202 return False
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203 # Check the subclass hook
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204 ok = cls.__subclasshook__(subclass)
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205 if ok is not NotImplemented:
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206 assert isinstance(ok, bool)
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207 if ok:
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208 cls._abc_cache.add(subclass)
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209 else:
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210 cls._abc_negative_cache.add(subclass)
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211 return ok
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212 # Check if it's a direct subclass
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213 if cls in getattr(subclass, '__mro__', ()):
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214 cls._abc_cache.add(subclass)
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215 return True
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216 # Check if it's a subclass of a registered class (recursive)
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217 for rcls in cls._abc_registry:
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218 if issubclass(subclass, rcls):
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219 cls._abc_cache.add(subclass)
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220 return True
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221 # Check if it's a subclass of a subclass (recursive)
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222 for scls in cls.__subclasses__():
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223 if issubclass(subclass, scls):
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224 cls._abc_cache.add(subclass)
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225 return True
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226 # No dice; update negative cache
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227 cls._abc_negative_cache.add(subclass)
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228 return False