78 lines
3.1 KiB
Python
78 lines
3.1 KiB
Python
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# Copyright 2009-2022 Joshua Bronson. All rights reserved.
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#
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# This Source Code Form is subject to the terms of the Mozilla Public
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# License, v. 2.0. If a copy of the MPL was not distributed with this
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# file, You can obtain one at http://mozilla.org/MPL/2.0/.
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# * Code review nav *
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# (see comments in __init__.py)
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#==============================================================================
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# ← Prev: __init__.py Current: _abc.py Next: _base.py →
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#==============================================================================
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"""Provide the :class:`BidirectionalMapping` abstract base class."""
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from __future__ import annotations
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from abc import abstractmethod
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import typing as t
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from ._typing import KT, VT
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class BidirectionalMapping(t.Mapping[KT, VT]):
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"""Abstract base class for bidirectional mapping types.
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Extends :class:`collections.abc.Mapping` primarily by adding the
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(abstract) :attr:`inverse` property,
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which implementors of :class:`BidirectionalMapping`
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should override to return a reference to the inverse
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:class:`BidirectionalMapping` instance.
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"""
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__slots__ = ()
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@property
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@abstractmethod
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def inverse(self) -> BidirectionalMapping[VT, KT]:
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"""The inverse of this bidirectional mapping instance.
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*See also* :attr:`bidict.BidictBase.inverse`, :attr:`bidict.BidictBase.inv`
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:raises NotImplementedError: Meant to be overridden in subclasses.
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"""
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# The @abstractmethod decorator prevents BidirectionalMapping subclasses from being
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# instantiated unless they override ``.inverse``. So this implementation of ``.inverse``
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# should never be unintentionally resolved from subclass instances. But raise here
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# anyway, so it's extra clear that this implementation should never be called.
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raise NotImplementedError
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def __inverted__(self) -> t.Iterator[tuple[VT, KT]]:
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"""Get an iterator over the items in :attr:`inverse`.
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This is functionally equivalent to iterating over the items in the
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forward mapping and inverting each one on the fly, but this provides a
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more efficient implementation: Assuming the already-inverted items
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are stored in :attr:`inverse`, just return an iterator over them directly.
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Providing this default implementation enables external functions,
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particularly :func:`~bidict.inverted`, to use this optimized
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implementation when available, instead of having to invert on the fly.
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*See also* :func:`bidict.inverted`
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"""
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return iter(self.inverse.items())
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class MutableBidirectionalMapping(BidirectionalMapping[KT, VT], t.MutableMapping[KT, VT]):
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"""Abstract base class for mutable bidirectional mapping types."""
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__slots__ = ()
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# * Code review nav *
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#==============================================================================
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# ← Prev: __init__.py Current: _abc.py Next: _base.py →
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#==============================================================================
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