[Python-Dev] itertools module

[Skip Montanaro]

    >> * imap() - It's not clear to me why it differs from map() other than
    >>   the fact that it's an iterator.

    Raymond> The other differences are that it stops with the shortest
    Raymond> iterable and doesn't accept None for a func argument.

I understand that.  I was questioning why with a name like "imap" you chose
to make it differ from map() in ways other than its iterator-ness.  The
other semantic differences make it more difficult to replace map() with
itertools.imap() than it might be.

    Raymond> Because one or more useful inputs are potentially infinite,
    Raymond> filling in Nones is less useful than stopping with the shortest
    Raymond> iterator.

Yes, but it still seems a gratuitous change from map() to me.

    >> * loopzip() - It's not clear why its next() method should return a
    >>   list instead of a tuple (again, a seemingly needless distiction
    >>   with its builtin counterpart, zip()).

    Raymond> I've wrestled with the one.  The short answer is that zip()
    Raymond> already does a pretty good job and that the only use for
    Raymond> loopzip() is super high speed looping.  To that end, reusing a
    Raymond> single list instead of allocating and building tuples is *much*
    Raymond> faster.

How do you know the caller doesn't squirrel away the list you returned on
the n-th iteration?  I don't see how you can safely reuse the same list.

Skip