Result of ``a is b''

David MacQuigg dmq at gain.com
Wed Mar 17 02:55:46 CET 2004


On Tue, 16 Mar 2004 18:00:04 -0500, cookedm+news at physics.mcmaster.ca
(David M. Cooke) wrote:

>Personally, almost all my uses of 'is' are of the form 'x is None' or
>'x is not None'.

Here are some more test results (averaging 10,000 evaluations in a
tight loop):

        time (sec)    %
Test 1: 3.68E-007   100.0 F is False
Test 2: 4.87E-007   132.1 F == False
Test 3: 3.71E-007   100.0 N is None
Test 4: 5.51E-007   148.6 N == None

The '== None' test is 49% slower than 'is None', but in absolute time,
the difference is only 180nec (on my new, but not top-speed PC).  So
it would take about 10 million of these comparisons in a short time to
make a noticable difference to the user.

I can't see where the 'is' test would *ever* be needed for the above
comparisons.

-- Dave




More information about the Python-list mailing list