On Tue, 02 May 2006 21:44:21 +0200, Boris Borcic wrote: > note that generators have no defined length - precisely because they feed > values one at a time while you need them all together to speak of a > length. The second expression will raise a TypeError because of that.
Er, yes. If I had actually run that code, I would have seen that error. Thank you for the correction. > If you want to count objects > with a generator expression, use > > sum(1 for v in seq if some_condition(v)) > > which is also clearer imho; summing ones for each item satisfying a > condition - isn't that a definition of counting ? That is indeed very clear and I like it. You could also use a function that counts all different values in a list, reducing the list to a dictionary whose keys are the unique values from the list. I got the idea from a discussion here on comp.lang.python; I called my version of it tally(). d = tally(bool(x) for x in seq) print d[True] # prints how many true values in seq print d[False] # prints how many false values in seq tally() is in my iterwrap.py module, which you can get here: http://home.blarg.net/~steveha/iterwrap.tar.gz -- Steve R. Hastings "Vita est" [EMAIL PROTECTED] http://www.blarg.net/~steveha -- http://mail.python.org/mailman/listinfo/python-list
