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annotate Lib/contextlib.py @ 64158:ea0decd2acfb

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Fix typo
author Éric Araujo <merwok@netwok.org>
date Wed, 18 Aug 2010 22:35:23 +0000
parents 30e1d8d08105
children c03f64c71b05
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 functools import wraps
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5 from warnings import warn
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6
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7 __all__ = ["contextmanager", "closing", "ContextDecorator"]
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8
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9
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10 class ContextDecorator(object):
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11 "A base class or mixin that enables context managers to work as decorators."
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12 def __call__(self, func):
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13 @wraps(func)
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14 def inner(*args, **kwds):
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15 with self:
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16 return func(*args, **kwds)
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17 return inner
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18
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19
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20 class GeneratorContextManager(ContextDecorator):
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21 """Helper for @contextmanager decorator."""
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22
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23 def __init__(self, gen):
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24 self.gen = gen
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25
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26 def __enter__(self):
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27 try:
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28 return next(self.gen)
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29 except StopIteration:
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30 raise RuntimeError("generator didn't yield")
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31
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32 def __exit__(self, type, value, traceback):
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33 if type is None:
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34 try:
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35 next(self.gen)
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36 except StopIteration:
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37 return
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38 else:
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39 raise RuntimeError("generator didn't stop")
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40 else:
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41 if value is None:
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42 # Need to force instantiation so we can reliably
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43 # tell if we get the same exception back
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44 value = type()
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45 try:
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46 self.gen.throw(type, value, traceback)
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47 raise RuntimeError("generator didn't stop after throw()")
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48 except StopIteration as exc:
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49 # Suppress the exception *unless* it's the same exception that
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50 # was passed to throw(). This prevents a StopIteration
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51 # raised inside the "with" statement from being suppressed
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52 return exc is not value
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53 except:
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54 # only re-raise if it's *not* the exception that was
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55 # passed to throw(), because __exit__() must not raise
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56 # an exception unless __exit__() itself failed. But throw()
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57 # has to raise the exception to signal propagation, so this
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58 # fixes the impedance mismatch between the throw() protocol
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59 # and the __exit__() protocol.
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60 #
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61 if sys.exc_info()[1] is not value:
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62 raise
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63
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64
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65 def contextmanager(func):
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66 """@contextmanager decorator.
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67
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68 Typical usage:
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69
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70 @contextmanager
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71 def some_generator(<arguments>):
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72 <setup>
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73 try:
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74 yield <value>
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75 finally:
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76 <cleanup>
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77
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78 This makes this:
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79
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80 with some_generator(<arguments>) as <variable>:
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81 <body>
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82
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83 equivalent to this:
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84
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85 <setup>
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86 try:
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87 <variable> = <value>
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88 <body>
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89 finally:
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90 <cleanup>
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91
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92 """
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93 @wraps(func)
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94 def helper(*args, **kwds):
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95 return GeneratorContextManager(func(*args, **kwds))
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96 return helper
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97
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98
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99 class closing(object):
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100 """Context to automatically close something at the end of a block.
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101
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102 Code like this:
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103
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104 with closing(<module>.open(<arguments>)) as f:
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105 <block>
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106
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107 is equivalent to this:
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108
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109 f = <module>.open(<arguments>)
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110 try:
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111 <block>
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112 finally:
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113 f.close()
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114
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115 """
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116 def __init__(self, thing):
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117 self.thing = thing
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118 def __enter__(self):
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119 return self.thing
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120 def __exit__(self, *exc_info):
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121 self.thing.close()