On Mon, 10 Mar 2008 07:39:25 -0700, Gary Herron wrote:
> If either is a surprise, then understand that the "is" operator should
> probably *never* be used with immutable types.
Carl Banks has already mentioned testing for None with "is". The standard
idiom for using mutable default arguments goes something like this:
def foo(arg=None):
if arg is None:
arg = []
do_something_with(arg)
Another standard idiom that requires "is":
sentinel = object() # a special value that isn't None
...
if something is sentinel:
blah blah blah
Mutable or immutable, it makes no difference: "is" is for testing
identity, == is for testing equality. If you need to test for identity,
use "is". If you need to test for equality, use ==.
--
Steven
--
http://mail.python.org/mailman/listinfo/python-list
