New submission from Χρήστος Γεωργίου (Christos Georgiou) <t...@users.sourceforge.net>:
(Discovered in that StackOverflow answer: http://stackoverflow.com/questions/3940518/3942509#3942509 ; check the comments too) operator.attrgetter in its simplest form (i.e. with a single non-dotted name) needs more time to execute than an equivalent lambda expression. Attached file so3940518.py runs a simple benchmark comparing: a list comprehension of plain attribute access; attrgetter; and lambda. I will append sample benchmark times at the end of the comment. Browsing Modules/operator.c, I noticed that the dotted_getattr function was using PyUnicode_Check and (possibly) splitting on dots on *every* call of the attrgetter, which I thought to be most inefficient. I changed the py3k-daily-snapshot source to make the PyUnicode_Check calls in the attrgetter_new function; also, I modified the algorithm to pre-parse the operator.attrgetter functions for possible dots in the names, in order for the dotted_getattr function to become speedier. The only “drawback” is that now operator.attrgetter raises a TypeError on creation, not on subsequent calls of the attrgetter object; this shouldn't be a compatibility problem. However, I obviously had to update both Doc/library/operator.rst and Lib/test/test_operator.py . I am not sure whether I should attach a zip/tar file with both the attachments (the sample benchmark and the diff); so I'll attach the diff in a further comment. On the Ubuntu server 9.10 where I made the changes, I ran the so3940518.py sample benchmark before and after the changes. Run before the changes (third column is seconds, less is better): list comp 0.40999999999999925 1000000 map attrgetter 1.3899999999999997 1000000 map lambda 1.0099999999999998 1000000 Run after the changes: list comp 0.40000000000000036 1000000 map attrgetter 0.5199999999999996 1000000 map lambda 0.96 1000000 ---------- assignee: d...@python components: Documentation, Library (Lib), Tests files: so3940518.py messages: 119247 nosy: d...@python, tzot priority: normal severity: normal status: open title: operator.attrgetter slower than lambda after adding dotted names ability versions: Python 3.2 Added file: http://bugs.python.org/file19310/so3940518.py _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue10160> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
