bazarr/libs/bidict/_abc.py

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# -*- coding: utf-8 -*-
# Copyright 2009-2019 Joshua Bronson. All Rights Reserved.
#
# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.
#==============================================================================
# * Welcome to the bidict source code *
#==============================================================================
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"""Provides the :class:`BidirectionalMapping` abstract base class."""
from .compat import Mapping, abstractproperty, iteritems
class BidirectionalMapping(Mapping): # pylint: disable=abstract-method,no-init
"""Abstract base class (ABC) for bidirectional mapping types.
Extends :class:`collections.abc.Mapping` primarily by adding the
(abstract) :attr:`inverse` property,
which implementors of :class:`BidirectionalMapping`
should override to return a reference to the inverse
:class:`BidirectionalMapping` instance.
"""
__slots__ = ()
@abstractproperty
def inverse(self):
"""The inverse of this bidirectional mapping instance.
*See also* :attr:`bidict.BidictBase.inverse`, :attr:`bidict.BidictBase.inv`
:raises NotImplementedError: Meant to be overridden in subclasses.
"""
# The @abstractproperty decorator prevents BidirectionalMapping subclasses from being
# instantiated unless they override this method. So users shouldn't be able to get to the
# point where they can unintentionally call this implementation of .inverse on something
# anyway. Could leave the method body empty, but raise NotImplementedError so it's extra
# clear there's no reason to call this implementation (e.g. via super() after overriding).
raise NotImplementedError
def __inverted__(self):
"""Get an iterator over the items in :attr:`inverse`.
This is functionally equivalent to iterating over the items in the
forward mapping and inverting each one on the fly, but this provides a
more efficient implementation: Assuming the already-inverted items
are stored in :attr:`inverse`, just return an iterator over them directly.
Providing this default implementation enables external functions,
particularly :func:`~bidict.inverted`, to use this optimized
implementation when available, instead of having to invert on the fly.
*See also* :func:`bidict.inverted`
"""
return iteritems(self.inverse)
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