This page needs to be reformatted
A small number of constants live in the built-in namespace. They are:
False value of the bool type. Assignments to
False are illegal and raise a SyntaxError.
True value of the bool type. Assignments to
True are illegal and raise a SyntaxError.
The sole value of the type
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.
Special value which should be returned by the binary special methods (e.g. eq(), lt(), add(), rsub(), etc.) to indicate that the operation is not implemented with respect to the other type; may be returned by the in-place binary special methods (e.g. imul(), iand(), etc.) for the same purpose. Its truth value is
Note: When a binary (or in-place) method returns
NotImplemented the interpreter will try the reflected operation on the other type (or some other fallback, depending on the operator). If all attempts return
NotImplemented, the interpreter will raise an appropriate exception. Incorrectly returning
NotImplemented will result in a misleading error message or the
NotImplemented value being returned to Python code. See Implementing the arithmetic operations for examples.
NotImplemented are not interchangeable, even though they have similar names and purposes. See
NotImplementedError for details on when to use it.
The same as the ellipsis literal
“...”. Special value used mostly in conjunction with extended slicing syntax for user-defined container data types.
This constant is
True if Python was not started with an
-O option. See also the assert statement.
Note: The names None,
__debug__ cannot be reassigned (assignments to them, even as an attribute name, raise SyntaxError), so they can be considered “
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.
- 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.
- Objects that when printed or called, print the text of copyright or credits, respectively.
- Object that when printed, prints the message “Type license() to see the full license text”, and when called, displays the full license text in a pager-like fashion (one screen at a time).