Mercurial > cpython-lru_cache-weakref

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Add use_weakref option to functools.lru_cache The use_weakref option makes lru_cache create weak references to the function arguments when creating the cache key, which prevents them from staying in the memory forever even after all other references to them are gone. This is a proof of concept for http://bugs.python.org/issue19859
author Radomir Dopieralski <devel@sheep.art.pl>
date Tue, 03 Dec 2013 16:02:48 +0100
parents 87d49e2cdd34
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 """Utilities for with-statement contexts. See PEP 343."""
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2
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3 import sys
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4 from collections import deque
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5 from functools import wraps
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6
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7 __all__ = ["contextmanager", "closing", "ContextDecorator", "ExitStack",
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8 "redirect_stdout", "suppress"]
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9
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10
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11 class ContextDecorator(object):
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12 "A base class or mixin that enables context managers to work as decorators."
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13
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14 def _recreate_cm(self):
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15 """Return a recreated instance of self.
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16
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17 Allows an otherwise one-shot context manager like
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18 _GeneratorContextManager to support use as
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19 a decorator via implicit recreation.
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20
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21 This is a private interface just for _GeneratorContextManager.
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22 See issue #11647 for details.
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23 """
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24 return self
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25
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26 def __call__(self, func):
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27 @wraps(func)
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28 def inner(*args, **kwds):
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29 with self._recreate_cm():
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30 return func(*args, **kwds)
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31 return inner
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32
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33
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34 class _GeneratorContextManager(ContextDecorator):
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35 """Helper for @contextmanager decorator."""
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36
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37 def __init__(self, func, *args, **kwds):
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38 self.gen = func(*args, **kwds)
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39 self.func, self.args, self.kwds = func, args, kwds
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40 # Issue 19330: ensure context manager instances have good docstrings
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41 doc = getattr(func, "__doc__", None)
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42 if doc is None:
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43 doc = type(self).__doc__
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44 self.__doc__ = doc
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45 # Unfortunately, this still doesn't provide good help output when
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46 # inspecting the created context manager instances, since pydoc
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47 # currently bypasses the instance docstring and shows the docstring
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48 # for the class instead.
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49 # See http://bugs.python.org/issue19404 for more details.
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50
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51 def _recreate_cm(self):
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52 # _GCM instances are one-shot context managers, so the
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53 # CM must be recreated each time a decorated function is
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54 # called
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55 return self.__class__(self.func, *self.args, **self.kwds)
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56
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57 def __enter__(self):
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58 try:
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59 return next(self.gen)
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60 except StopIteration:
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61 raise RuntimeError("generator didn't yield") from None
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62
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63 def __exit__(self, type, value, traceback):
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64 if type is None:
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65 try:
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66 next(self.gen)
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67 except StopIteration:
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68 return
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69 else:
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70 raise RuntimeError("generator didn't stop")
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71 else:
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72 if value is None:
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73 # Need to force instantiation so we can reliably
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74 # tell if we get the same exception back
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75 value = type()
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76 try:
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77 self.gen.throw(type, value, traceback)
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78 raise RuntimeError("generator didn't stop after throw()")
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79 except StopIteration as exc:
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80 # Suppress the exception *unless* it's the same exception that
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81 # was passed to throw(). This prevents a StopIteration
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82 # raised inside the "with" statement from being suppressed
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83 return exc is not value
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84 except:
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85 # only re-raise if it's *not* the exception that was
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86 # passed to throw(), because __exit__() must not raise
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87 # an exception unless __exit__() itself failed. But throw()
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88 # has to raise the exception to signal propagation, so this
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89 # fixes the impedance mismatch between the throw() protocol
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90 # and the __exit__() protocol.
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91 #
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92 if sys.exc_info()[1] is not value:
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93 raise
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94
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95
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96 def contextmanager(func):
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97 """@contextmanager decorator.
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98
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99 Typical usage:
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100
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101 @contextmanager
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102 def some_generator(<arguments>):
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103 <setup>
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104 try:
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105 yield <value>
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106 finally:
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107 <cleanup>
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108
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109 This makes this:
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110
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111 with some_generator(<arguments>) as <variable>:
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112 <body>
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113
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114 equivalent to this:
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115
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116 <setup>
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117 try:
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118 <variable> = <value>
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119 <body>
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120 finally:
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121 <cleanup>
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122
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123 """
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124 @wraps(func)
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125 def helper(*args, **kwds):
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126 return _GeneratorContextManager(func, *args, **kwds)
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127 return helper
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128
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129
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130 class closing(object):
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131 """Context to automatically close something at the end of a block.
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132
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133 Code like this:
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134
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135 with closing(<module>.open(<arguments>)) as f:
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136 <block>
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137
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138 is equivalent to this:
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139
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140 f = <module>.open(<arguments>)
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141 try:
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142 <block>
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143 finally:
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144 f.close()
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145
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146 """
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147 def __init__(self, thing):
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148 self.thing = thing
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149 def __enter__(self):
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150 return self.thing
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151 def __exit__(self, *exc_info):
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152 self.thing.close()
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153
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154 class redirect_stdout:
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155 """Context manager for temporarily redirecting stdout to another file
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156
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157 # How to send help() to stderr
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158 with redirect_stdout(sys.stderr):
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159 help(dir)
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160
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161 # How to write help() to a file
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162 with open('help.txt', 'w') as f:
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163 with redirect_stdout(f):
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164 help(pow)
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165 """
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166
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167 def __init__(self, new_target):
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168 self._new_target = new_target
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169 # We use a list of old targets to make this CM re-entrant
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170 self._old_targets = []
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171
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172 def __enter__(self):
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173 self._old_targets.append(sys.stdout)
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174 sys.stdout = self._new_target
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175 return self._new_target
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176
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177 def __exit__(self, exctype, excinst, exctb):
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178 sys.stdout = self._old_targets.pop()
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179
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180
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181 class suppress:
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182 """Context manager to suppress specified exceptions
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183
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184 After the exception is suppressed, execution proceeds with the next
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185 statement following the with statement.
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186
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187 with suppress(FileNotFoundError):
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188 os.remove(somefile)
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189 # Execution still resumes here if the file was already removed
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190 """
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191
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192 def __init__(self, *exceptions):
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193 self._exceptions = exceptions
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194
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195 def __enter__(self):
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196 pass
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197
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198 def __exit__(self, exctype, excinst, exctb):
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199 # Unlike isinstance and issubclass, CPython exception handling
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200 # currently only looks at the concrete type hierarchy (ignoring
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201 # the instance and subclass checking hooks). While Guido considers
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202 # that a bug rather than a feature, it's a fairly hard one to fix
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203 # due to various internal implementation details. suppress provides
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204 # the simpler issubclass based semantics, rather than trying to
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205 # exactly reproduce the limitations of the CPython interpreter.
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206 #
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207 # See http://bugs.python.org/issue12029 for more details
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208 return exctype is not None and issubclass(exctype, self._exceptions)
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209
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210
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211 # Inspired by discussions on http://bugs.python.org/issue13585
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212 class ExitStack(object):
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213 """Context manager for dynamic management of a stack of exit callbacks
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214
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215 For example:
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216
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217 with ExitStack() as stack:
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218 files = [stack.enter_context(open(fname)) for fname in filenames]
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219 # All opened files will automatically be closed at the end of
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220 # the with statement, even if attempts to open files later
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221 # in the list raise an exception
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222
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223 """
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224 def __init__(self):
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225 self._exit_callbacks = deque()
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226
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227 def pop_all(self):
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228 """Preserve the context stack by transferring it to a new instance"""
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229 new_stack = type(self)()
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230 new_stack._exit_callbacks = self._exit_callbacks
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231 self._exit_callbacks = deque()
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232 return new_stack
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233
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234 def _push_cm_exit(self, cm, cm_exit):
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235 """Helper to correctly register callbacks to __exit__ methods"""
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236 def _exit_wrapper(*exc_details):
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237 return cm_exit(cm, *exc_details)
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238 _exit_wrapper.__self__ = cm
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239 self.push(_exit_wrapper)
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240
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241 def push(self, exit):
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242 """Registers a callback with the standard __exit__ method signature
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243
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244 Can suppress exceptions the same way __exit__ methods can.
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245
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246 Also accepts any object with an __exit__ method (registering a call
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247 to the method instead of the object itself)
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248 """
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249 # We use an unbound method rather than a bound method to follow
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250 # the standard lookup behaviour for special methods
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251 _cb_type = type(exit)
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252 try:
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253 exit_method = _cb_type.__exit__
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254 except AttributeError:
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255 # Not a context manager, so assume its a callable
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256 self._exit_callbacks.append(exit)
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257 else:
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258 self._push_cm_exit(exit, exit_method)
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259 return exit # Allow use as a decorator
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260
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261 def callback(self, callback, *args, **kwds):
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262 """Registers an arbitrary callback and arguments.
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263
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264 Cannot suppress exceptions.
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265 """
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266 def _exit_wrapper(exc_type, exc, tb):
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267 callback(*args, **kwds)
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268 # We changed the signature, so using @wraps is not appropriate, but
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269 # setting __wrapped__ may still help with introspection
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270 _exit_wrapper.__wrapped__ = callback
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271 self.push(_exit_wrapper)
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272 return callback # Allow use as a decorator
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273
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274 def enter_context(self, cm):
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275 """Enters the supplied context manager
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276
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277 If successful, also pushes its __exit__ method as a callback and
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278 returns the result of the __enter__ method.
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279 """
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280 # We look up the special methods on the type to match the with statement
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281 _cm_type = type(cm)
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282 _exit = _cm_type.__exit__
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283 result = _cm_type.__enter__(cm)
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284 self._push_cm_exit(cm, _exit)
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285 return result
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286
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287 def close(self):
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288 """Immediately unwind the context stack"""
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289 self.__exit__(None, None, None)
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290
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291 def __enter__(self):
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292 return self
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293
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294 def __exit__(self, *exc_details):
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295 received_exc = exc_details[0] is not None
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296
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297 # We manipulate the exception state so it behaves as though
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298 # we were actually nesting multiple with statements
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299 frame_exc = sys.exc_info()[1]
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300 def _fix_exception_context(new_exc, old_exc):
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301 while 1:
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302 exc_context = new_exc.__context__
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303 if exc_context in (None, frame_exc):
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304 break
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305 new_exc = exc_context
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306 new_exc.__context__ = old_exc
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307
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308 # Callbacks are invoked in LIFO order to match the behaviour of
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309 # nested context managers
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310 suppressed_exc = False
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311 pending_raise = False
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312 while self._exit_callbacks:
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313 cb = self._exit_callbacks.pop()
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314 try:
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315 if cb(*exc_details):
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316 suppressed_exc = True
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317 pending_raise = False
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318 exc_details = (None, None, None)
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319 except:
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320 new_exc_details = sys.exc_info()
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321 # simulate the stack of exceptions by setting the context
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322 _fix_exception_context(new_exc_details[1], exc_details[1])
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323 pending_raise = True
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324 exc_details = new_exc_details
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325 if pending_raise:
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326 try:
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327 # bare "raise exc_details[1]" replaces our carefully
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328 # set-up context
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329 fixed_ctx = exc_details[1].__context__
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330 raise exc_details[1]
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331 except BaseException:
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332 exc_details[1].__context__ = fixed_ctx
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333 raise
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334 return received_exc and suppressed_exc