Source code for bidict._frozenbidict

# -*- coding: utf-8 -*-
# Copyright 2009-2019 Joshua Bronson. All Rights Reserved.
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# License, v. 2.0. If a copy of the MPL was not distributed with this
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"""Provides :class:`frozenbidict`, an immutable, hashable bidirectional mapping type."""

from ._base import BidictBase
from ._delegating_mixins import _DelegateKeysAndItemsToFwdm
from .compat import ItemsView


class frozenbidict(_DelegateKeysAndItemsToFwdm, BidictBase):  # noqa: N801,E501; pylint: disable=invalid-name
    """Immutable, hashable bidict type."""

    __slots__ = ()

    def __hash__(self):  # lgtm [py/equals-hash-mismatch]
        """The hash of this bidict as determined by its items."""
        if getattr(self, '_hash', None) is None:
            # pylint: disable=protected-access,attribute-defined-outside-init
            self._hash = ItemsView(self)._hash()
        return self._hash


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