4. Built-in Constants¶
A small number of constants live in the built-in namespace. They are:
The sole value of
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 a
Special value used in conjunction with extended slicing syntax.
Changed in version 2.7: Assignments to
__debug__ as an attribute became illegal.
site module (which is imported automatically during startup, except
-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.
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.