8000 bpo-43245: Add keyword argument support to ChainMap.new_child() (GH-2… · python/cpython@9923df9 · GitHub
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bpo-43245: Add keyword argument support to ChainMap.new_child() (GH-24788)
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‎Doc/library/collections.rst

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@@ -72,19 +72,23 @@ The class can be used to simulate nested scopes and is useful in templating.
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be modified to change which mappings are searched. The list should
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always contain at least one mapping.
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.. method:: new_child(m=None)
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.. method:: new_child(m=None, **kwargs)
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Returns a new :class:`ChainMap` containing a new map followed by
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all of the maps in the current instance. If ``m`` is specified,
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it becomes the new map at the front of the list of mappings; if not
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specified, an empty dict is used, so that a call to ``d.new_child()``
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is equivalent to: ``ChainMap({}, *d.maps)``. This method is used for
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creating subcontexts that can be updated without altering values in any
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of the parent mappings.
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is equivalent to: ``ChainMap({}, *d.maps)``. If any keyword arguments
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are specified, they update passed map or new empty dict. This method
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is used for creating subcontexts that can be updated without altering
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values in any of the parent mappings.
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.. versionchanged:: 3.4
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The optional ``m`` parameter was added.
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.. versionchanged:: 3.10
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Keyword arguments support was added.
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.. attribute:: parents
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Property returning a new :class:`ChainMap` containing all of the maps in

‎Lib/collections/__init__.py

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@@ -1010,12 +1010,15 @@ def copy(self):
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__copy__ = copy
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def new_child(self, m=None): # like Django's Context.push()
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def new_child(self, m=None, **kwargs): # like Django's Context.push()
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'''New ChainMap with a new map followed by all previous maps.
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If no map is provided, an empty dict is used.
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Keyword arguments update the map or new empty dict.
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'''
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if m is None:
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m = {}
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m = kwargs
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elif kwargs:
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m.update(kwargs)
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return self.__class__(m, *self.maps)
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@property

‎Lib/test/test_collections.py

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for k, v in dict(a=1, B=20, C=30, z=100).items(): # check get
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self.assertEqual(d.get(k, 100), v)
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c = ChainMap({'a': 1, 'b': 2})
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d = c.new_child(b=20, c=30)
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self.assertEqual(d.maps, [{'b': 20, 'c': 30}, {'a': 1, 'b': 2}])
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def test_union_operators(self):
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cm1 = ChainMap(dict(a=1, b=2), dict(c=3, d=4))
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cm2 = ChainMap(dict(a=10, e=5), dict(b=20, d=4))

‎Misc/NEWS.d/next/Library/2021-03-08-22-14-37.bpo-43245.nXL-MC.rst

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Add keyword arguments support to ``ChainMap.new_child()``.

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