A small number of constants live in the built-in namespace. They are:
Noneis frequently used to represent the absence of a value, as when default arguments are not passed to a function. Assignments to
Noneare illegal and raise a
Special value which should be returned by the binary special methods
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
__iand__(), etc.) for the same purpose.
It should not be evaluated in a boolean context.
When a binary (or in-place) method returns
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.
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.
NotImplementedError for details on when to use it.
...”. Special value used mostly in conjunction with extended slicing syntax for user-defined container data types.
-Ooption. See also the
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.
SystemExitwith the specified exit code.