<var> is None vs. <var> == None
steve at REMOVE-THIS-cybersource.com.au
Sat Jan 24 00:49:11 CET 2009
On Fri, 23 Jan 2009 14:58:34 -0500, Gerald Britton wrote:
> Hi -- Some time ago I ran across a comment recommending using <var> is
> None instead of <var> == None (also <var> is not None, etc.)
That entirely depends on whether you wish to test for something which
*is* None or something with *equals* None. Those two things have
I wonder, do newbies actually get the impression from somewhere that "is"
is a synonym for "=="?
> My own
> testing indicates that the former beats the latter by about 30% on
> average. Not a log for a single instruction but it can add up in large
If you have a "large" project where the time taken to do comparisons to
None is a significant portion of the total time, I'd be very surprised.
var is None is a micro-optimization, but that's not why we do it. We do
it because usually the correct test is whether var *is* None and not
merely equal to None. Any random object might happen to equal None
(admittedly most objects don't), but only None is None.
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