On Oct 18, 10:21 am, Hrvoje Niksic <[EMAIL PROTECTED]> wrote: > Paul Hankin <[EMAIL PROTECTED]> writes: > > On Oct 17, 10:03 pm, 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? > > > Use a += b rather than a.extend(b): I'm not sure what I was > > thinking. > > Why? a.extend(b) is at least as readable, and is guaranteed to extend > the same list. In general, "a += b" can fall back to the slower "a = > a + b" for sequences that don't support +=.
Not to me: I can never remember which of a.append and a.extend is which. Falling back to a = a + b is exactly what you want. For instance: a = (1, 2, 3) a += (4, 5, 6) works, whereas: a = (1, 2, 3) a.extend((4, 5, 6)) doesn't. So using += makes your code more general. There's no standard sequence type that has extend and not +=, so worrying that += is slower isn't a concern unless you're using a user-defined class. Even then, it's probably a mistake that should be fixed in the class rather than requiring .extend() to be used instead of +=. -- Paul Hankin -- http://mail.python.org/mailman/listinfo/python-list
