3. Built-in Constants
A small number of constants live in the built-in namespace. They are:
-
False
- The false value of the bool type. Assignments to False
are illegal and raise a SyntaxError.
-
True
- The true value of the bool type. Assignments to True
are illegal and raise a SyntaxError.
-
None
- The sole value of types.NoneType. None is 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 SyntaxError.
-
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
The same as .... Special value used mostly in conjunction with extended
slicing syntax for user-defined container data types, as in
.. XXX Someone who understands extended slicing should fill in here.
-
__debug__
- This constant is true if Python was not started with an -O option.
Assignments to __debug__ are illegal and raise a SyntaxError.
See also the assert statement.
3.1. 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 SystemExit with the
specified exit code.
-
copyright
-
license
-
credits
- Objects that when printed, print a message like “Type license() to see the
full license text”, and when called, display the corresponding text in a
pager-like fashion (one screen at a time).
