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import collections |
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import itertools |
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class DictStack(list, collections.abc.Mapping): |
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""" |
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A stack of dictionaries that behaves as a view on those dictionaries, |
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giving preference to the last. |
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>>> stack = DictStack([dict(a=1, c=2), dict(b=2, a=2)]) |
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>>> stack['a'] |
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2 |
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>>> stack['b'] |
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2 |
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>>> stack['c'] |
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2 |
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>>> len(stack) |
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3 |
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>>> stack.push(dict(a=3)) |
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>>> stack['a'] |
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3 |
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>>> set(stack.keys()) == set(['a', 'b', 'c']) |
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True |
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>>> set(stack.items()) == set([('a', 3), ('b', 2), ('c', 2)]) |
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True |
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>>> dict(**stack) == dict(stack) == dict(a=3, c=2, b=2) |
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True |
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>>> d = stack.pop() |
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>>> stack['a'] |
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2 |
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>>> d = stack.pop() |
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>>> stack['a'] |
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1 |
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>>> stack.get('b', None) |
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>>> 'c' in stack |
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True |
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""" |
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def __iter__(self): |
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dicts = list.__iter__(self) |
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return iter(set(itertools.chain.from_iterable(c.keys() for c in dicts))) |
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def __getitem__(self, key): |
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for scope in reversed(tuple(list.__iter__(self))): |
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if key in scope: |
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return scope[key] |
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raise KeyError(key) |
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push = list.append |
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def __contains__(self, other): |
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return collections.abc.Mapping.__contains__(self, other) |
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def __len__(self): |
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return len(list(iter(self))) |
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