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bpo-42487: don't call __getitem__ of underlying maps in ChainMap.__iter__ (GH-23534)

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Andreas Poehlmann 2020-11-30 17:34:15 +01:00 • committed by GitHub
parent 9f004634a2
commit 0be9ce305f
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3 changed files with 18 additions and 1 deletions
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16
Lib/test/test_collections.py
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@ -196,6 +196,22 @@ class TestChainMap(unittest.TestCase):
('e', 55), ('f', 666), ('g', 777), ('h', 88888),
('i', 9999), ('j', 0)])
def test_iter_not_calling_getitem_on_maps(self):
class DictWithGetItem(UserDict):
def __init__(self, *args, **kwds):
self.called = False
UserDict.__init__(self, *args, **kwds)
def __getitem__(self, item):
self.called = True
UserDict.__getitem__(self, item)
d = DictWithGetItem(a=1)
c = ChainMap(d)
d.called = False
set(c) # iterate over chain map
self.assertFalse(d.called, '__getitem__ was called')
def test_dict_coercion(self):
d = ChainMap(dict(a=1, b=2), dict(b=20, c=30))
self.assertEqual(dict(d), dict(a=1, b=2, c=30))