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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/.
"""Useful functions for working with bidirectional mappings and related data."""
from itertools import chain, repeat
from .compat import iteritems, Mapping
_NULL_IT = repeat(None, 0) # repeat 0 times -> raise StopIteration from the start
def _iteritems_mapping_or_iterable(arg):
"""Yield the items in *arg*.
If *arg* is a :class:`~collections.abc.Mapping`, return an iterator over its items.
Otherwise return an iterator over *arg* itself.
"""
return iteritems(arg) if isinstance(arg, Mapping) else iter(arg)
def _iteritems_args_kw(*args, **kw):
"""Yield the items from the positional argument (if given) and then any from *kw*.
:raises TypeError: if more than one positional argument is given.
"""
args_len = len(args)
if args_len > 1:
raise TypeError('Expected at most 1 positional argument, got %d' % args_len)
itemchain = None
if args:
arg = args[0]
if arg:
itemchain = _iteritems_mapping_or_iterable(arg)
if kw:
iterkw = iteritems(kw)
itemchain = chain(itemchain, iterkw) if itemchain else iterkw
return itemchain or _NULL_IT
def inverted(arg):
"""Yield the inverse items of the provided object.
If *arg* has a :func:`callable` ``__inverted__`` attribute,
return the result of calling it.
Otherwise, return an iterator over the items in `arg`,
inverting each item on the fly.
*See also* :attr:`bidict.BidirectionalMapping.__inverted__`
"""
inv = getattr(arg, '__inverted__', None)
if callable(inv):
return inv()
return ((val, key) for (key, val) in _iteritems_mapping_or_iterable(arg))
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