mirror of https://github.com/jab/bidict.git
28 lines
755 B
PHP
28 lines
755 B
PHP
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frozenbidict
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------------
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Having :class:`bidict.BidirectionalMapping`
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extend the Mapping ABC rather than MutableMapping
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allows for an *immutable* bidict type to extend from *it*.
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This type is called :class:`bidict.frozenbidict`,
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and makes up the other branch of the tree.
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As you would expect,
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attempting to mutate a frozenbidict after initializing it causes an error::
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>>> f = frozenbidict()
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>>> f['C'] = 'carbon'
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Traceback (most recent call last):
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...
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TypeError...
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Besides extending BidirectionalMapping,
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frozenbidict implements :class:`collections.abc.Hashable`.
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Thus it's suitable for insertion into sets or other maps::
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>>> f = frozenbidict()
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>>> set([f]) is not 'an error'
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True
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as expected of an immutable type.
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