Built-in Constants — Python v3.0.1 documentation
A small number of constants live in the built-in namespace. They are:
Note
None, False, True and __debug__ cannot be reassigned (assignments to them raise SyntaxError), so they can be considered “true” constants.
- 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.
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, and when .