Markus wrote:
> You know you're guilty of early/over optimisation, when it's almost two
> in the morning and the file open in front of you reads as follows.
>
> The code you are about to read is real...
> Some of the variable names have been changed
> to protect the families of those involved.
>
> [-snip-]
>
> from timeit import Timer
>
> if __name__=='__main__':
> t = Timer('len(argv)==1','from sys import argv')
> print "%f usec/pass" % (1000000 * t.timeit(number=100000)/100000)
> t = Timer('argv[0]==argv[-1]','from sys import argv')
> print "%f usec/pass" % (1000000 * t.timeit(number=100000)/100000)
>
> [-snip-]
>
> For anyone is in danger of making the same mistakes I've made...
> the results were:
>
> 0.219154 usec/pass
> 0.297468 usec/pass
>
>
> If anyone doesn't understand...
> Timer is a "Class for timing execution speed of small code snippets."
> The quoted description of Timer and the original code I derived the
> above snippet from, can be found in the Python documentation.
>
> Finally, for anyone who is wondering...
> I will seek help as soon as I have some free time.
>
Do you realise that the two expressions that you are comparing are not
even equivalent, and moreover you ignored an expression that will be
faster and equivalent (unless/until somebody decides on an
"optimisation" like interning/sharing strings between/among sys.argv
elements).
C:\junk>type showargs.py
from sys import argv
print argv, len(argv)==1, argv[0]==argv[-1], argv[0] is argv[-1]
C:\junk>showargs.py C:\junk\showargs.py
['C:\\junk\\showargs.py', 'C:\\junk\\showargs.py'] False True False
C:\junk>python -mtimeit -s"a=['jabberwocky','jabber'+'wocky']"
"len(a)==1"
1000000 loops, best of 3: 0.142 usec per loop
C:\junk>python -mtimeit -s"a=['jabberwocky','jabber'+'wocky']"
"a[0]==a[-1]"
1000000 loops, best of 3: 0.191 usec per loop
C:\junk>python -mtimeit -s"a=['jabberwocky','jabber'+'wocky']" "a[0] is
a[-1]"
10000000 loops, best of 3: 0.135 usec per loop
C:\junk>python -mtimeit -s"a=['jabberwocky']" "len(a)==1"
1000000 loops, best of 3: 0.132 usec per loop
C:\junk>python -mtimeit -s"a=['jabberwocky']" "a[0]==a[-1]"
1000000 loops, best of 3: 0.14 usec per loop
C:\junk>python -mtimeit -s"a=['jabberwocky']" "a[0] is a[-1]"
1000000 loops, best of 3: 0.111 usec per loop
Cheers,
John
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