47 lines
1.8 KiB
Python
47 lines
1.8 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: _base.py Current: _frozenbidict.py Next: _bidict.py →
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#==============================================================================
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"""Provide :class:`frozenbidict`, an immutable, hashable bidirectional mapping type."""
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from __future__ import annotations
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import typing as t
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from ._base import BidictBase
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from ._typing import KT, VT
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class frozenbidict(BidictBase[KT, VT]):
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"""Immutable, hashable bidict type."""
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_hash: int
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# Work around lack of support for higher-kinded types in Python.
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# Ref: https://github.com/python/typing/issues/548#issuecomment-621571821
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if t.TYPE_CHECKING:
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@property
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def inverse(self) -> frozenbidict[VT, KT]: ...
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def __hash__(self) -> int:
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"""The hash of this bidict as determined by its items."""
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if getattr(self, '_hash', None) is None:
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# The following is like hash(frozenset(self.items()))
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# but more memory efficient. See also: https://bugs.python.org/issue46684
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self._hash = t.ItemsView(self)._hash()
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return self._hash
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# * Code review nav *
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#==============================================================================
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# ← Prev: _base.py Current: _frozenbidict.py Next: _bidict.py →
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#==============================================================================
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