When to use None
Bernhard Herzog
herzog at online.de
Wed Feb 2 08:23:27 EST 2000
Laurence Tratt <tratt at dcs.kcl.ac.uk> writes:
> stevie_deja at my-deja.com wrote:
>
> > Would anyone explain to me where there is a difference between the
> > following two calls:
> >
> > if some_var == None : print 'var is none'
> >
> > if some_var is None : print 'var is none'
> >
> > Can '== None' only be used in certain circumstances?
>
> In this particular circumstance, both lines of code will always produce the
> same result;
Whether they're equivalent depends on what some_var actually is. If it's
a class instance whose class implements the __cmp__ method it may well
be equal but not identical to None:
>>> class C:
.. def __cmp__(self, other):
.. return cmp(None, other)
..
>>> c = C()
>>> c == None
1
>>> c is None
0
>>>
--
Bernhard Herzog | Sketch, a drawing program for Unix
herzog at online.de | http://sketch.sourceforge.net/
More information about the Python-list
mailing list