On Oct 18, 9:47 am, [EMAIL PROTECTED] (Alex Martelli) wrote: > Debajit Adhikary <[EMAIL PROTECTED]> wrote: > > > How does "a.extend(b)" compare with "a += b" when it comes to > > performance? Does a + b create a completely new list that it assigns > > back to a? If so, a.extend(b) would seem to be faster. How could I > > verify things like these? > > That's what the timeit module is for, but make sure that the snippet > you're timing has no side effects (since it's repeatedly executed). > E.g.: > > brain:~ alex$ python -mtimeit -s'z=[1,2,3];b=[4,5,6]' > 'a=z[:];a.extend(b)' > 1000000 loops, best of 3: 0.769 usec per loop > brain:~ alex$ python -mtimeit -s'z=[1,2,3];b=[4,5,6]' 'a=z[:];a+=b' > 1000000 loops, best of 3: 0.664 usec per loop > brain:~ alex$ python -mtimeit -s'z=[1,2,3];b=[4,5,6]' > 'a=z[:];a.extend(b)' > 1000000 loops, best of 3: 0.769 usec per loop > brain:~ alex$ python -mtimeit -s'z=[1,2,3];b=[4,5,6]' 'a=z[:];a+=b' > 1000000 loops, best of 3: 0.665 usec per loop > brain:~ alex$ > > The repetition of the measurements show them very steady, so now you > know that += is about 100 nanoseconds faster (on my laptop) than extend > (the reason is: it saves the tiny cost of looking up 'extend' on a; to > verify this, use much longer lists and you'll notice that while overall > times for both approaches increase, the difference between the two > approaches remains about the same for lists of any length).
> You can find more details on commandline use of timeit at > <http://docs.python.org/lib/node808.html> (see adjacent nodes in Python > docs for examples and details on the more advanced use of timeit inside > your own code) but I hope these indications may be of help anyway. Thanks for the wonderful explanation on timeit. Thats one more tool now in my arsenal :P -- http://mail.python.org/mailman/listinfo/python-list
