mirror of https://github.com/jab/bidict.git
77 lines
2.0 KiB
ReStructuredText
77 lines
2.0 KiB
ReStructuredText
.. _other-bidict-types:
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Other bidict Types
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==================
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Now that we've covered
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:class:`bidict.bidict`,
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:class:`bidict.loosebidict`,
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and some other basics,
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let's look at the remaining bidict types
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and the hierarchy they belong to.
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bidict Class Hierarchy
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----------------------
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.. image:: _static/class-hierarchy.svg
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:alt: bidict class hierarchy
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At the top of the bidict type hierarchy is
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:class:`bidict.BidirectionalMapping`.
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This implements the :class:`collections.abc.Mapping` ABC
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and contains the shared logic allowing keys to be looked up by value
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(as well as values to be looked up by key).
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Most users will only ever need to use one of its subclasses.
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At this point the type hierarchy tree forks into
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a mutable branch and an immutable branch.
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On the mutable side we have
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:class:`bidict.bidict`
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(which implements :class:`collections.abc.MutableMapping`)
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and finally
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:class:`bidict.loosebidict`,
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the leaf on this side of the tree.
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.. include:: frozenbidict.doctest.rst.inc
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.. include:: orderedbidict.doctest.rst.inc
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.. include:: namedbidict.doctest.rst.inc
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Polymorphism
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------------
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Note that none of the bidict types inherit from dict::
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>>> from bidict import bidict, frozenbidict
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>>> isinstance(bidict(), dict)
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False
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>>> isinstance(frozenbidict(), dict)
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False
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If you must use :func:`isinstance` to check whether a bidict is dict-like,
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you can use the abstract base classes from the :mod:`collections` module,
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which is a better way to check for interface conformance::
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>>> from collections import Mapping, MutableMapping
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>>> isinstance(bidict(), MutableMapping)
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True
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>>> isinstance(frozenbidict(), Mapping)
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True
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Though you can often write more polymorphic code
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by using duck typing rather than :func:`isinstance`::
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>>> mystery = object()
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>>> try:
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... mystery[0] = 1
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... except TypeError:
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... pass
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>>> mystery2 = object()
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>>> if hasattr(mystery2, '__setitem__'):
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... mystery2[0] = 1
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There's one more bit of functionality to cover,
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the :ref:`inverted` iterator.
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