On Fri, May 6, 2016 at 12:46 PM, Dan Sommers <d...@tombstonezero.net> wrote: > filter used to build a list, but now it doesn't (where "used to" means > Python 2.7 and "now" means Python 3.5; I'm too lazy to track down the > exact point(s) at which it changed): > > Python 2.7.11+ (default, Apr 17 2016, 14:00:29) > [GCC 5.3.1 20160409] on linux2 > Type "help", "copyright", "credits" or "license" for more information. > >>> filter(lambda x:x+1, [1, 2, 3, 4]) > [1, 2, 3, 4] > > Python 3.5.1+ (default, Apr 17 2016, 16:14:06) > [GCC 5.3.1 20160409] on linux > Type "help", "copyright", "credits" or "license" for more information. > >>> filter(lambda x:x+1, [1, 2, 3, 4]) > <filter object at 0x7f26a9ef3320>
Most of these kinds of changes happened in 3.0, where backward-incompatible changes were accepted. A whole bunch of things stopped returning lists and started returning lazy iterables - range, filter/map, dict.keys(), etc - because most of the time, they're iterated over once and then dropped. ChrisA -- https://mail.python.org/mailman/listinfo/python-list
