1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
|
from __future__ import annotations
from abc import ABCMeta, abstractmethod
from typing import Callable, Iterable, Union
__all__ = ["Filter", "Never", "Always", "Condition", "FilterOrBool"]
class Filter(metaclass=ABCMeta):
"""
Base class for any filter to activate/deactivate a feature, depending on a
condition.
The return value of ``__call__`` will tell if the feature should be active.
"""
def __init__(self) -> None:
self._and_cache: dict[Filter, Filter] = {}
self._or_cache: dict[Filter, Filter] = {}
self._invert_result: Filter | None = None
@abstractmethod
def __call__(self) -> bool:
"""
The actual call to evaluate the filter.
"""
return True
def __and__(self, other: Filter) -> Filter:
"""
Chaining of filters using the & operator.
"""
assert isinstance(other, Filter), "Expecting filter, got %r" % other
if isinstance(other, Always):
return self
if isinstance(other, Never):
return other
if other in self._and_cache:
return self._and_cache[other]
result = _AndList.create([self, other])
self._and_cache[other] = result
return result
def __or__(self, other: Filter) -> Filter:
"""
Chaining of filters using the | operator.
"""
assert isinstance(other, Filter), "Expecting filter, got %r" % other
if isinstance(other, Always):
return other
if isinstance(other, Never):
return self
if other in self._or_cache:
return self._or_cache[other]
result = _OrList.create([self, other])
self._or_cache[other] = result
return result
def __invert__(self) -> Filter:
"""
Inverting of filters using the ~ operator.
"""
if self._invert_result is None:
self._invert_result = _Invert(self)
return self._invert_result
def __bool__(self) -> None:
"""
By purpose, we don't allow bool(...) operations directly on a filter,
because the meaning is ambiguous.
Executing a filter has to be done always by calling it. Providing
defaults for `None` values should be done through an `is None` check
instead of for instance ``filter1 or Always()``.
"""
raise ValueError(
"The truth value of a Filter is ambiguous. "
"Instead, call it as a function."
)
def _remove_duplicates(filters: list[Filter]) -> list[Filter]:
result = []
for f in filters:
if f not in result:
result.append(f)
return result
class _AndList(Filter):
"""
Result of &-operation between several filters.
"""
def __init__(self, filters: list[Filter]) -> None:
super().__init__()
self.filters = filters
@classmethod
def create(cls, filters: Iterable[Filter]) -> Filter:
"""
Create a new filter by applying an `&` operator between them.
If there's only one unique filter in the given iterable, it will return
that one filter instead of an `_AndList`.
"""
filters_2: list[Filter] = []
for f in filters:
if isinstance(f, _AndList): # Turn nested _AndLists into one.
filters_2.extend(f.filters)
else:
filters_2.append(f)
# Remove duplicates. This could speed up execution, and doesn't make a
# difference for the evaluation.
filters = _remove_duplicates(filters_2)
# If only one filter is left, return that without wrapping into an
# `_AndList`.
if len(filters) == 1:
return filters[0]
return cls(filters)
def __call__(self) -> bool:
return all(f() for f in self.filters)
def __repr__(self) -> str:
return "&".join(repr(f) for f in self.filters)
class _OrList(Filter):
"""
Result of |-operation between several filters.
"""
def __init__(self, filters: list[Filter]) -> None:
super().__init__()
self.filters = filters
@classmethod
def create(cls, filters: Iterable[Filter]) -> Filter:
"""
Create a new filter by applying an `|` operator between them.
If there's only one unique filter in the given iterable, it will return
that one filter instead of an `_OrList`.
"""
filters_2: list[Filter] = []
for f in filters:
if isinstance(f, _OrList): # Turn nested _AndLists into one.
filters_2.extend(f.filters)
else:
filters_2.append(f)
# Remove duplicates. This could speed up execution, and doesn't make a
# difference for the evaluation.
filters = _remove_duplicates(filters_2)
# If only one filter is left, return that without wrapping into an
# `_AndList`.
if len(filters) == 1:
return filters[0]
return cls(filters)
def __call__(self) -> bool:
return any(f() for f in self.filters)
def __repr__(self) -> str:
return "|".join(repr(f) for f in self.filters)
class _Invert(Filter):
"""
Negation of another filter.
"""
def __init__(self, filter: Filter) -> None:
super().__init__()
self.filter = filter
def __call__(self) -> bool:
return not self.filter()
def __repr__(self) -> str:
return "~%r" % self.filter
class Always(Filter):
"""
Always enable feature.
"""
def __call__(self) -> bool:
return True
def __or__(self, other: Filter) -> Filter:
return self
def __invert__(self) -> Never:
return Never()
class Never(Filter):
"""
Never enable feature.
"""
def __call__(self) -> bool:
return False
def __and__(self, other: Filter) -> Filter:
return self
def __invert__(self) -> Always:
return Always()
class Condition(Filter):
"""
Turn any callable into a Filter. The callable is supposed to not take any
arguments.
This can be used as a decorator::
@Condition
def feature_is_active(): # `feature_is_active` becomes a Filter.
return True
:param func: Callable which takes no inputs and returns a boolean.
"""
def __init__(self, func: Callable[[], bool]) -> None:
super().__init__()
self.func = func
def __call__(self) -> bool:
return self.func()
def __repr__(self) -> str:
return "Condition(%r)" % self.func
# Often used as type annotation.
FilterOrBool = Union[Filter, bool]
|
