Coverage for python / lsst / daf / butler / nonempty_mapping.py: 44%

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/>. 

27 

28from __future__ import annotations 

29 

30__all__ = ("NonemptyMapping",) 

31 

32from collections.abc import Callable, Iterator, Mapping 

33from typing import Any, Protocol, Self, TypeVar, overload 

34 

35 

36class Copyable(Protocol): 

37 def copy(self) -> Self: ... 37 ↛ exitline 37 didn't return from function 'copy' because

38 

39 

40_K = TypeVar("_K") 

41_T = TypeVar("_T") 

42_V = TypeVar("_V", bound=Copyable, covariant=True) 

43 

44 

45class NonemptyMapping(Mapping[_K, _V]): 

46 """A `~collections.abc.Mapping` that implicitly adds values (like 

47 `~collections.defaultdict`) but treats any that evaluate to `False` as not 

48 present. 

49 

50 Parameters 

51 ---------- 

52 default_factory : `~collections.abc.Callable` 

53 A callable that takes no arguments and returns a new instance of the 

54 value type. 

55 

56 Notes 

57 ----- 

58 Unlike `~collections.defaultdict`, this class implements only 

59 `collections.abc.Mapping`, not `~collections.abc.MutableMapping`, and hence 

60 it can be modified only by invoking ``__getitem__`` with a key that does 

61 not exist. It is expected that the value type will be a mutable container 

62 like `set` or `dict`, and that an empty nested container should be 

63 considered equivalent to the absence of a key. The value type must have 

64 a `copy` method that copies all mutable state. 

65 """ 

66 

67 def __init__(self, default_factory: Callable[[], _V]) -> None: 

68 self._mapping: dict[_K, _V] = {} 

69 self._next: _V = default_factory() 

70 self._default_factory = default_factory 

71 

72 def __len__(self) -> int: 

73 return sum(bool(v) for v in self._mapping.values()) 

74 

75 def __iter__(self) -> Iterator[_K]: 

76 for key, values in self._mapping.items(): 

77 if values: 

78 yield key 

79 

80 def __getitem__(self, key: _K) -> _V: 

81 # We use setdefault with an existing empty inner container (_next), 

82 # since we expect that to usually return an existing object and we 

83 # don't want the overhead of making a new inner container each time. 

84 # When we do insert _next, we replace it. 

85 if (value := self._mapping.setdefault(key, self._next)) is self._next: 

86 self._next = self._default_factory() 

87 return value 

88 

89 # We don't let Mapping implement `__contains__` or `get` for us, because we 

90 # don't want the side-effect of adding an empty inner container from 

91 # calling `__getitem__`. 

92 

93 def __contains__(self, key: Any) -> bool: 

94 return bool(self._mapping.get(key)) 

95 

96 @overload 

97 def get(self, key: _K) -> _V | None: ... 97 ↛ exitline 97 didn't return from function 'get' because

98 

99 @overload 

100 def get(self, key: _K, default: _T) -> _V | _T: ... 100 ↛ exitline 100 didn't return from function 'get' because

101 

102 def get(self, key: _K, default: Any = None) -> Any: 

103 if value := self._mapping.get(key): 

104 return value 

105 return default 

106 

107 def copy(self) -> NonemptyMapping[_K, _V]: 

108 """Return a copy of the mapping. 

109 

110 This deep-copies values while referencing the ``default_factory`` 

111 callback and keys. 

112 """ 

113 result = NonemptyMapping[_K, _V](self._default_factory) 

114 for k, v in self._mapping.items(): 

115 result._mapping[k] = v.copy() 

116 return result