.. and here's my original reply to Nick, which was also intended to go to the list. Sorry, folks.
Mark ---------- Forwarded message ---------- From: Mark Dickinson <dicki...@gmail.com> Date: Mon, Dec 27, 2010 at 10:27 AM Subject: Re: [Python-Dev] Range __contains__ and objects with __index__ methods To: Nick Coghlan <ncogh...@gmail.com> On Mon, Dec 27, 2010 at 12:15 AM, Nick Coghlan <ncogh...@gmail.com> wrote: > Starting in Python 3.2, range() supports fast containment checking for > integers (i.e. based on an O(1) arithmetic calculation rather than an > O(N) iteration through the entire sequence). > > Currently, this fast path ignores objects that implement __index__ - > they are relegated to the slow iterative search. > > This seems wrong to me [...] Is seems to me that there are two separate issues here. Namely, (1) Determine the semantics of 'x in range(...)' for an object x that implements __index__, and (2) implement the containment check efficiently. At the moment, it looks as though the __index__ method is ignored entirely for the containment check, so you're proposing a change in semantics. If/when that change in semantics is made, fixing up the code to do the containment check efficiently seems like it should be a straightforward task. With the proposed change in semantics, the simple definition (x in range(...) iff x == y for some element y of range(...)) no longer holds. I'm not convinced (but not unconvinced either) that it's worth breaking that simplicity. Mark _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
