
Built-in Constants
******************

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.

copyright
license
credits

   Objects that when printed, print a message like "Type license() to
   see the full license text", and when called, display the
   corresponding text in a pager-like fashion (one screen at a time).
