On Thu, Oct 18, 2012 at 8:42 PM, Demian Brecht <demianbre...@gmail.com> wrote: >> str, bytes, bytearrays, arrays, sets, frozensets, dicts, dictviews, and >> ranges should all return len in O(1) time. That includes the possibility >> of a subtraction as indicated above. > > Awesome. Pretty much what I figured. Of course, I'll have to dig around the > source just to confirm this with my own eyes (more just curiosity than > anything), so if you know whereabouts to look, it would be most helpful :)
The source is usually in Objects/*object.c (e.g., the source for list is in Objects/listobject.c, dict is in dictobject.c and so on). The implementation of __len__ is usually in a method called whatever_length (e.g., dict.__len__ is called dict_length). To be sure, you can check the PyTypeObject declaration for the type. Probably the tp_as_sequence or tp_as_mapping field contains the pointer to __len__ (sq_length or mp_length respectively). (You can also search for "lenfunc", which is the type of such functions.) -- http://mail.python.org/mailman/listinfo/python-list