Mercurial > hg
view mercurial/thirdparty/jaraco/collections.py @ 50408:82e5a9b1ef1e
extras: re-use Projection from jaraco.collections
author | Jason R. Coombs <jaraco@jaraco.com> |
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date | Tue, 21 Mar 2023 20:47:30 -0400 |
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# adapted from jaraco.collections 3.9 import collections class Projection(collections.abc.Mapping): """ Project a set of keys over a mapping >>> sample = {'a': 1, 'b': 2, 'c': 3} >>> prj = Projection(['a', 'c', 'd'], sample) >>> prj == {'a': 1, 'c': 3} True Keys should only appear if they were specified and exist in the space. >>> sorted(list(prj.keys())) ['a', 'c'] Attempting to access a key not in the projection results in a KeyError. >>> prj['b'] Traceback (most recent call last): ... KeyError: 'b' Use the projection to update another dict. >>> target = {'a': 2, 'b': 2} >>> target.update(prj) >>> target == {'a': 1, 'b': 2, 'c': 3} True Also note that Projection keeps a reference to the original dict, so if you modify the original dict, that could modify the Projection. >>> del sample['a'] >>> dict(prj) {'c': 3} """ def __init__(self, keys, space): self._keys = tuple(keys) self._space = space def __getitem__(self, key): if key not in self._keys: raise KeyError(key) return self._space[key] def __iter__(self): return iter(set(self._keys).intersection(self._space)) def __len__(self): return len(tuple(iter(self)))