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
|
.. _built-in-consts:
Built-in Constants
==================
A small number of constants live in the built-in namespace. They are:
.. data:: False
The false value of the :class:`bool` type. Assignments to ``False``
are illegal and raise a :exc:`SyntaxError`.
.. data:: True
The true value of the :class:`bool` type. Assignments to ``True``
are illegal and raise a :exc:`SyntaxError`.
.. data:: None
An object frequently used to represent the absence of a value, as when
default arguments are not passed to a function. Assignments to ``None``
are illegal and raise a :exc:`SyntaxError`.
``None`` is the sole instance of the :data:`~types.NoneType` type.
.. data:: NotImplemented
A special value which should be returned by the binary special methods
(e.g. :meth:`~object.__eq__`, :meth:`~object.__lt__`, :meth:`~object.__add__`, :meth:`~object.__rsub__`,
etc.) to indicate that the operation is not implemented with respect to
the other type; may be returned by the in-place binary special methods
(e.g. :meth:`~object.__imul__`, :meth:`~object.__iand__`, etc.) for the same purpose.
It should not be evaluated in a boolean context.
:data:`!NotImplemented` is the sole instance of the :data:`types.NotImplementedType` type.
.. note::
When a binary (or in-place) method returns :data:`!NotImplemented` the
interpreter will try the reflected operation on the other type (or some
other fallback, depending on the operator). If all attempts return
:data:`!NotImplemented`, the interpreter will raise an appropriate exception.
Incorrectly returning :data:`!NotImplemented` will result in a misleading
error message or the :data:`!NotImplemented` value being returned to Python code.
See :ref:`implementing-the-arithmetic-operations` for examples.
.. note::
``NotImplementedError`` and :data:`!NotImplemented` are not interchangeable,
even though they have similar names and purposes.
See :exc:`NotImplementedError` for details on when to use it.
.. versionchanged:: 3.9
Evaluating :data:`!NotImplemented` in a boolean context is deprecated. While
it currently evaluates as true, it will emit a :exc:`DeprecationWarning`.
It will raise a :exc:`TypeError` in a future version of Python.
.. index:: single: ...; ellipsis literal
.. data:: Ellipsis
The same as the ellipsis literal "``...``". Special value used mostly in conjunction
with extended slicing syntax for user-defined container data types.
``Ellipsis`` is the sole instance of the :data:`types.EllipsisType` type.
.. data:: __debug__
This constant is true if Python was not started with an :option:`-O` option.
See also the :keyword:`assert` statement.
.. note::
The names :data:`None`, :data:`False`, :data:`True` and :data:`__debug__`
cannot be reassigned (assignments to them, even as an attribute name, raise
:exc:`SyntaxError`), so they can be considered "true" constants.
Constants added by the :mod:`site` module
-----------------------------------------
The :mod:`site` module (which is imported automatically during startup, except
if the :option:`-S` command-line option is given) adds several constants to the
built-in namespace. They are useful for the interactive interpreter shell and
should not be used in programs.
.. data:: quit(code=None)
exit(code=None)
Objects that when printed, print a message like "Use quit() or Ctrl-D
(i.e. EOF) to exit", and when called, raise :exc:`SystemExit` with the
specified exit code.
.. data:: copyright
credits
Objects that when printed or called, print the text of copyright or
credits, respectively.
.. data:: license
Object that when printed, prints the message "Type license() to see the
full license text", and when called, displays the full license text in a
pager-like fashion (one screen at a time).
|
