grscheller.untyped.nothing

A nothing is an attempt to give Python a "bottom" type.

unlike a true bottom, it can be instantiated as a singleton
types like ~T|None and ~T|() act like a poor man's Optional/Maybe Monads
both None and () make for lousy bottom types
both don't accept many methods, None has no length, at least () is iterable
when returning or iterating values, both must constantly be checked for
many developers use None and () as sentinel values
therefore by design Null & () are store-able in this data structure

View Source

 1# Copyright 2023-2024 Geoffrey R. Scheller
 2#
 3# Licensed under the Apache License, Version 2.0 (the "License");
 4# you may not use this file except in compliance with the License.
 5# You may obtain a copy of the License at
 6#
 7#     http://www.apache.org/licenses/LICENSE-2.0
 8#
 9# Unless required by applicable law or agreed to in writing, software
10# distributed under the License is distributed on an "AS IS" BASIS,
11# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12# See the License for the specific language governing permissions and
13# limitations under the License.
14
15"""A nothing is an attempt to give Python a "bottom" type.
16
17* unlike a true bottom, it can be instantiated as a singleton
18* types like ~T|None and ~T|() act like a poor man's Optional/Maybe Monads
19* both None and () make for lousy bottom types
20* both don't accept many methods, None has no length, at least () is iterable
21* when returning or iterating values, both must constantly be checked for
22* many developers use None and () as sentinel values
23* therefore by design Null & () are store-able in this data structure
24
25"""
26
27from __future__ import annotations
28
29__all__ = [ 'Nothing', 'nothing' ]
30__author__ = "Geoffrey R. Scheller"
31__copyright__ = "Copyright (c) 2023-2024 Geoffrey R. Scheller"
32__license__ = "Apache License 2.0"
33
34from typing import Any, Callable, Iterator, Optional
35
36class Nothing():
37    """Singleton semantically represents a missing value.
38
39    * nothing: Nothing = Nothing() is a singleton representing an absent value
40    * returns itself for arbitrary method calls
41    * returns itself if called as a Callable with arbitrary arguments
42    * interpreted as an empty container by standard Python functions
43    * makes for a better "bottom type" than either None or ()
44    """
45    __slots__ = ()
46
47    def __new__(cls) -> Nothing:
48        if not hasattr(cls, 'instance'):
49            cls.instance = super(Nothing, cls).__new__(cls)
50        return cls.instance
51
52    def __iter__(self) -> Iterator[Any]:
53        return iter(())
54
55    def __repr__(self) -> str:
56        return 'nothing'
57
58    def __bool__(self) -> bool:
59        return False
60
61    def __len__(self) -> int:
62        return 0
63
64    def __add__(self, right: Any) -> Any:
65        return Nothing()
66
67    def __radd__(self, left: Any) -> Any:
68        return Nothing()
69
70    def __mul__(self, right: Any) -> Any:
71        return Nothing()
72
73    def __rmul__(self, left: Any) -> Any:
74        return Nothing()
75
76    def __getitem__(self, index: int|slice) -> Any:
77        return Nothing()
78
79    def __setitem__(self, index: int|slice, item: Any) -> None:
80        return
81
82  # def __getattr__(self, name: str) -> Callable[[Any], Any]:
83  #     """pdoc gags on this commented-out code when generating docs"""
84  #     def method(*args: Any, **kwargs: Any) -> Any:
85  #         return Nothing()
86  #     return method
87
88    def __call__(*args: Any, **kwargs: Any) -> Any:
89        return Nothing()
90
91    def get(self, alt: Optional[Any]=(None, (13, 7), None, 42424242)) -> Any:
92        """Returns an alternate value, defaults Nothing()."""
93        if alt == (None, (13, 7), None, 42424242):  # an unlikely sentinel value
94            return Nothing()
95        else:
96            return alt
97
98nothing = Nothing()

class Nothing: View Source

37class Nothing():
38    """Singleton semantically represents a missing value.
39
40    * nothing: Nothing = Nothing() is a singleton representing an absent value
41    * returns itself for arbitrary method calls
42    * returns itself if called as a Callable with arbitrary arguments
43    * interpreted as an empty container by standard Python functions
44    * makes for a better "bottom type" than either None or ()
45    """
46    __slots__ = ()
47
48    def __new__(cls) -> Nothing:
49        if not hasattr(cls, 'instance'):
50            cls.instance = super(Nothing, cls).__new__(cls)
51        return cls.instance
52
53    def __iter__(self) -> Iterator[Any]:
54        return iter(())
55
56    def __repr__(self) -> str:
57        return 'nothing'
58
59    def __bool__(self) -> bool:
60        return False
61
62    def __len__(self) -> int:
63        return 0
64
65    def __add__(self, right: Any) -> Any:
66        return Nothing()
67
68    def __radd__(self, left: Any) -> Any:
69        return Nothing()
70
71    def __mul__(self, right: Any) -> Any:
72        return Nothing()
73
74    def __rmul__(self, left: Any) -> Any:
75        return Nothing()
76
77    def __getitem__(self, index: int|slice) -> Any:
78        return Nothing()
79
80    def __setitem__(self, index: int|slice, item: Any) -> None:
81        return
82
83  # def __getattr__(self, name: str) -> Callable[[Any], Any]:
84  #     """pdoc gags on this commented-out code when generating docs"""
85  #     def method(*args: Any, **kwargs: Any) -> Any:
86  #         return Nothing()
87  #     return method
88
89    def __call__(*args: Any, **kwargs: Any) -> Any:
90        return Nothing()
91
92    def get(self, alt: Optional[Any]=(None, (13, 7), None, 42424242)) -> Any:
93        """Returns an alternate value, defaults Nothing()."""
94        if alt == (None, (13, 7), None, 42424242):  # an unlikely sentinel value
95            return Nothing()
96        else:
97            return alt

Singleton semantically represents a missing value.

nothing: Nothing = Nothing() is a singleton representing an absent value
returns itself for arbitrary method calls
returns itself if called as a Callable with arbitrary arguments
interpreted as an empty container by standard Python functions
makes for a better "bottom type" than either None or ()

def get(self, alt: Optional[Any] = (None, (13, 7), None, 42424242)) -> Any: View Source

92    def get(self, alt: Optional[Any]=(None, (13, 7), None, 42424242)) -> Any:
93        """Returns an alternate value, defaults Nothing()."""
94        if alt == (None, (13, 7), None, 42424242):  # an unlikely sentinel value
95            return Nothing()
96        else:
97            return alt

Returns an alternate value, defaults Nothing().

instance = nothing

nothing = nothing