I'll let this short and sweet PEP speak for itself.
http://python.sourceforge.net/peps/pep-0285.html
PEP: 285
Title: Adding a bool type
Version: $Revision: 1.1 $
Last-Modified: $Date: 2002/03/08 15:38:37 $
Author: guido@python.org (Guido van Rossum)
Status: Draft
Type: Standards Track
Created: 8-Mar-2002
Python-Version: 2.3
Post-History: 8-Mar-2002 (python-dev)
Abstract
This PEP proposes the introduction of a new built-in type, bool,
with two constants, False and True. The bool type would be a
straightforward subtype (in C) of the int type, and the values
False and True would behave like 0 and 1 in most respects (e.g.
False==0 and True==1 would be true) except repr() and str(). All
built-in operations that conceptually return a Boolean result will
be changed to return False or True instead of 0 or 1; for example,
comparisons and the "not" operator.
Rationale
Most languages eventually grow a Boolean type; even C99 has one.
It's useful to be able to tell from a function result that the
outcome has Boolean semantics.
Specification
The following Python code specifies most of the properties of the
new type:
class bool(int):
def __new__(cls, val=0, _create=0):
if _create:
# This is nor part of the spec,
# just a hack to bootstrap False and True
return int.__new__(cls, not not val)
elif val:
return True
else:
return False
def __repr__(self):
if self:
return "True"
else:
return "False"
__str__ = __repr__
def __and__(self, other):
if isinstance(other, bool):
return bool(int(self) & int(other))
else:
return NotImplemented
__rand__ = __and__
def __or__(self, other):
if isinstance(other, bool):
return bool(int(self) | int(other))
else:
return NotImplemented
__ror__ = __or__
def __xor__(self, other):
if isinstance(other, bool):
return bool(int(self) ^ int(other))
else:
return NotImplemented
__rxor__ = __xor__
False = bool(0, _create=1)
True = bool(1, _create=1)
Issues
Because the repr() or str() of a bool value is different from an
int value, some code (e.g. doctest-based unit tests) may fail.
How much of a backwards compatibility problem this will be, I
don't know. If we find this is a real problem, we could add a
command-line option to make False and True aliases for 0 and 1 and
bool an alias for int.
Copyright
This document has been placed in the public domain.
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End:
--Guido van Rossum (home page: http://www.python.org/~guido/)
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