mirror of https://github.com/python/cpython
Fix indentation.
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Georg Brandl
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@ -91,65 +91,66 @@ The class can be used to simulate nested scopes and is useful in templating.
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The use-cases also parallel those for the builtin :func:`super` function.
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A reference to ``d.parents`` is equivalent to: ``ChainMap(*d.maps[1:])``.
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.. versionadded:: 3.3
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.. versionadded:: 3.3
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Example of simulating Python's internal lookup chain::
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Example of simulating Python's internal lookup chain::
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import builtins
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pylookup = ChainMap(locals(), globals(), vars(builtins))
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import builtins
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pylookup = ChainMap(locals(), globals(), vars(builtins))
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Example of letting user specified values take precedence over environment
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variables which in turn take precedence over default values::
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Example of letting user specified values take precedence over environment
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variables which in turn take precedence over default values::
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import os, argparse
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defaults = {'color': 'red', 'user': guest}
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parser = argparse.ArgumentParser()
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parser.add_argument('-u', '--user')
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parser.add_argument('-c', '--color')
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user_specified = vars(parser.parse_args())
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combined = ChainMap(user_specified, os.environ, defaults)
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import os, argparse
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defaults = {'color': 'red', 'user': guest}
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parser = argparse.ArgumentParser()
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parser.add_argument('-u', '--user')
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parser.add_argument('-c', '--color')
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user_specified = vars(parser.parse_args())
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combined = ChainMap(user_specified, os.environ, defaults)
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Example patterns for using the :class:`ChainMap` class to simulate nested
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contexts::
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Example patterns for using the :class:`ChainMap` class to simulate nested
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contexts::
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c = ChainMap() Create root context
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d = c.new_child() Create nested child context
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e = c.new_child() Child of c, independent from d
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e.maps[0] Current context dictionary -- like Python's locals()
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e.maps[-1] Root context -- like Python's globals()
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e.parents Enclosing context chain -- like Python's nonlocals
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c = ChainMap() # Create root context
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d = c.new_child() # Create nested child context
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e = c.new_child() # Child of c, independent from d
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e.maps[0] # Current context dictionary -- like Python's locals()
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e.maps[-1] # Root context -- like Python's globals()
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e.parents # Enclosing context chain -- like Python's nonlocals
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d['x'] Get first key in the chain of contexts
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d['x'] = 1 Set value in current context
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del['x'] Delete from current context
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list(d) All nested values
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k in d Check all nested values
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len(d) Number of nested values
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d.items() All nested items
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dict(d) Flatten into a regular dictionary
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d['x'] # Get first key in the chain of contexts
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d['x'] = 1 # Set value in current context
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del['x'] # Delete from current context
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list(d) # All nested values
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k in d # Check all nested values
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len(d) # Number of nested values
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d.items() # All nested items
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dict(d) # Flatten into a regular dictionary
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.. seealso::
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.. seealso::
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* The `MultiContext class
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<http://svn.enthought.com/svn/enthought/CodeTools/trunk/enthought/contexts/multi_context.py>`_
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in the Enthought `CodeTools package
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<https://github.com/enthought/codetools>`_ has options to support
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writing to any mapping in the chain.
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* The `MultiContext class
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<http://svn.enthought.com/svn/enthought/CodeTools/trunk/enthought/contexts/multi_context.py>`_
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in the Enthought `CodeTools package
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<https://github.com/enthought/codetools>`_ has options to support
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writing to any mapping in the chain.
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* Django's `Context class
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<http://code.djangoproject.com/browser/django/trunk/django/template/context.py>`_
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for templating is a read-only chain of mappings. It also features
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pushing and popping of contexts similar to the
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:meth:`~collections.ChainMap.new_child` method and the
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:meth:`~collections.ChainMap.parents` property.
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* Django's `Context class
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<http://code.djangoproject.com/browser/django/trunk/django/template/context.py>`_
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for templating is a read-only chain of mappings. It also features
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pushing and popping of contexts similar to the
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:meth:`~collections.ChainMap.new_child` method and the
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:meth:`~collections.ChainMap.parents` property.
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* The `Nested Contexts recipe
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<http://code.activestate.com/recipes/577434/>`_ has options to control
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whether writes and other mutations apply only to the first mapping or to
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any mapping in the chain.
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* The `Nested Contexts recipe
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<http://code.activestate.com/recipes/577434/>`_ has options to control
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whether writes and other mutations apply only to the first mapping or to
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any mapping in the chain.
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* A `greatly simplified read-only version of Chainmap
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<http://code.activestate.com/recipes/305268/>`_.
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* A `greatly simplified read-only version of Chainmap
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<http://code.activestate.com/recipes/305268/>`_.
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:class:`Counter` objects
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------------------------
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