When to use None
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
>>> c is None
Bernhard Herzog | Sketch, a drawing program for Unix
herzog at online.de | http://sketch.sourceforge.net/
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