Coverage for python/lsst/daf/butler/nonempty_mapping.py: 46%
32 statements
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1# This file is part of daf_butler.
2#
3# Developed for the LSST Data Management System.
4# This product includes software developed by the LSST Project
5# (http://www.lsst.org).
6# See the COPYRIGHT file at the top-level directory of this distribution
7# for details of code ownership.
8#
9# This software is dual licensed under the GNU General Public License and also
10# under a 3-clause BSD license. Recipients may choose which of these licenses
11# to use; please see the files gpl-3.0.txt and/or bsd_license.txt,
12# respectively. If you choose the GPL option then the following text applies
13# (but note that there is still no warranty even if you opt for BSD instead):
14#
15# This program is free software: you can redistribute it and/or modify
16# it under the terms of the GNU General Public License as published by
17# the Free Software Foundation, either version 3 of the License, or
18# (at your option) any later version.
19#
20# This program is distributed in the hope that it will be useful,
21# but WITHOUT ANY WARRANTY; without even the implied warranty of
22# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
23# GNU General Public License for more details.
24#
25# You should have received a copy of the GNU General Public License
26# along with this program. If not, see <http://www.gnu.org/licenses/>.
28from __future__ import annotations
30__all__ = ("NonemptyMapping",)
32from collections.abc import Callable, Iterator, Mapping
33from typing import Any, TypeVar, overload
35_K = TypeVar("_K")
36_T = TypeVar("_T")
37_V = TypeVar("_V", covariant=True)
40class NonemptyMapping(Mapping[_K, _V]):
41 """A `Mapping` that implicitly adds values (like
42 `~collections.defaultdict`) but treats any that evaluate to `False` as not
43 present.
45 Parameters
46 ----------
47 default_factory : `~collections.abc.Callable`
48 A callable that takes no arguments and returns a new instance of the
49 value type.
51 Notes
52 -----
53 Unlike `~collections.defaultdict`, this class implements only
54 `collections.abc.Mapping`, not `~collections.abc.MutableMapping`, and hence
55 it can be modified only by invoking ``__getitem__`` with a key that does
56 not exist. It is expected that the value type will be a mutable container
57 like `set` or `dict`, and that an empty nested container should be
58 considered equivalent to the absence of a key.
59 """
61 def __init__(self, default_factory: Callable[[], _V]) -> None:
62 self._mapping: dict[_K, _V] = {}
63 self._next: _V = default_factory()
64 self._default_factory = default_factory
66 def __len__(self) -> int:
67 return sum(bool(v) for v in self._mapping.values())
69 def __iter__(self) -> Iterator[_K]:
70 for key, values in self._mapping.items():
71 if values:
72 yield key
74 def __getitem__(self, key: _K) -> _V:
75 # We use setdefault with an existing empty inner container (_next),
76 # since we expect that to usually return an existing object and we
77 # don't want the overhead of making a new inner container each time.
78 # When we do insert _next, we replace it.
79 if (value := self._mapping.setdefault(key, self._next)) is self._next:
80 self._next = self._default_factory()
81 return value
83 # We don't let Mapping implement `__contains__` or `get` for us, because we
84 # don't want the side-effect of adding an empty inner container from
85 # calling `__getitem__`.
87 def __contains__(self, key: Any) -> bool:
88 return bool(self._mapping.get(key))
90 @overload
91 def get(self, key: _K) -> _V | None: ... 91 ↛ exitline 91 didn't return from function 'get', because
93 @overload
94 def get(self, key: _K, default: _T) -> _V | _T: ... 94 ↛ exitline 94 didn't return from function 'get', because
96 def get(self, key: _K, default: Any = None) -> Any:
97 if value := self._mapping.get(key):
98 return value
99 return default