106 lines
4.5 KiB
Python
106 lines
4.5 KiB
Python
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# -*- coding: utf-8 -*-
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# Copyright 2009-2020 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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#==============================================================================
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# * Welcome to the bidict source code *
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#==============================================================================
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# Doing a code review? You'll find a "Code review nav" comment like the one
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# below at the top and bottom of the most important source files. This provides
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# a suggested initial path through the source when reviewing.
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#
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# Note: If you aren't reading this on https://github.com/jab/bidict, you may be
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# viewing an outdated version of the code. Please head to GitHub to review the
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# latest version, which contains important improvements over older versions.
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#
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# Thank you for reading and for any feedback you provide.
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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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"""Provide the :class:`BidirectionalMapping` abstract base class."""
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import typing as _t
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from abc import abstractmethod
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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 (ABC) 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 @abstractproperty decorator prevents BidirectionalMapping subclasses from being
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# instantiated unless they override this method. So users shouldn't be able to get to the
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# point where they can unintentionally call this implementation of .inverse on something
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# anyway. Could leave the method body empty, but raise NotImplementedError so it's extra
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# clear there's no reason to call this implementation (e.g. via super() after overriding).
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raise NotImplementedError
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def __inverted__(self) -> _t.Iterator[_t.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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def values(self) -> _t.AbstractSet[VT]: # type: ignore # https://github.com/python/typeshed/issues/4435
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"""A set-like object providing a view on the contained values.
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Override the implementation inherited from
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:class:`~collections.abc.Mapping`.
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Because the values of a :class:`~bidict.BidirectionalMapping`
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are the keys of its inverse,
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this returns a :class:`~collections.abc.KeysView`
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rather than a :class:`~collections.abc.ValuesView`,
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which has the advantages of constant-time containment checks
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and supporting set operations.
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"""
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return self.inverse.keys()
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class MutableBidirectionalMapping(BidirectionalMapping[KT, VT], _t.MutableMapping[KT, VT]):
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"""Abstract base class (ABC) 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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