#!/usr/bin/env python
# -*- coding: utf-8 -*-
#
# frozenordereddict.py
"""
Provides FrozenOrderedDict, an immutable ordered dictionary.
"""
#
# Copyright (c) 2020 Dominic Davis-Foster <dominic@davis-foster.co.uk>
# Copyright (c) 2015 Warren Smith
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU Lesser General Public License as published by
# the Free Software Foundation; either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU Lesser General Public License for more details.
#
# You should have received a copy of the GNU Lesser General Public License
# along with this program; if not, write to the Free Software
# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
# MA 02110-1301, USA.
#
# stdlib
import operator
from collections import OrderedDict
from functools import reduce
# this package
from .base import FrozenBase, KT, VT
[docs]class FrozenOrderedDict(FrozenBase[KT, VT]):
"""
An immutable OrderedDict.
It can be used as a drop-in replacement for dictionaries where immutability is desired.
"""
dict_cls = OrderedDict # type: ignore
def __init__(self, *args, **kwargs):
if hasattr(self, "_dict"):
raise TypeError(f"`{self.__class__}` can only be initialised once.")
super().__init__(*args, **kwargs)
[docs] def copy(self, *args, **kwargs):
new_dict = self._dict.copy()
if args or kwargs:
new_dict.update(OrderedDict(*args, **kwargs))
return self.__class__(new_dict)
def __hash__(self) -> int:
if self._hash is None:
self._hash = reduce(operator.xor, map(hash, self.items()), 0)
return self._hash