4. Built-in Constants¶
A small number of constants live in the built-in namespace. They are:
A small number of constants live in the built-in namespace. They are:
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.
Changed in version 2.4:
Changed in version 2.4: 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¶Special value used in conjunction with extended slicing syntax.
__debug__¶This constant is true if Python was not started with an -O option.
It cannot be reassigned. See also the assert statement.
Note
The name None cannot be reassigned (assignments to it, even as an
attribute name, raise SyntaxError), so it can be considered a “true”
constant.
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.