4. Built-in Constants¶
A small number of constants live in the built-in namespace. They are:
-
None¶ The sole value of
types.NoneType.Noneis frequently used to represent the absence of a value, as when default arguments are not passed to a function.Changed in version 2.4: Assignments to
Noneare illegal and raise aSyntaxError.
-
NotImplemented¶ Special value which can be returned by the “rich comparison” special methods (
__eq__(),__lt__(), and friends), to indicate that the comparison is not implemented with respect to the other type.
-
Ellipsis¶ Special value used in conjunction with extended slicing syntax.
-
__debug__¶ This constant is true if Python was not started with an
-Ooption. See also theassertstatement.
Note
The names None and __debug__ cannot be reassigned
(assignments to them, even as an attribute name, raise SyntaxError),
so they can be considered “true” constants.
Changed in version 2.7: Assignments to __debug__ as an attribute became illegal.
4.1. Constants added by the site module¶
The site module (which is imported automatically during startup, except
if the -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.
-
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
SystemExitwith the specified exit code.
