On Wed, Nov 18, 2009 at 4:51 PM, GoodPotatoes <goodpotat...@yahoo.com> wrote: > I'm dealing with bigger lists than I have been, and noticed this is getting > really slow. Is there a faster way to do this? > > for x in list1: > if x not in list2: > list3.append(x) > > My search is taking up to 5 minutes to complete.
If you can, use a set instead of list2. "x not in list2" does a linear search of list2 for x, which takes time proportional to the length of list2. Searching a set takes constant time - it doesn't depend on the size of the set. Also you can use a list comprehension to speed up the outer loop a little: set_of_list2 = set(list2) list3 = [ x for x in list1 if x not in set_of_list2 ] Note this will only work if the elements of list2 are hashable (useable as dict keys). Kent _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
