New submission from Serhiy Storchaka: In some circumstances iterating dict under 3.6 can be 20% slower than under 3.5.
$ ./python -m perf timeit -s "d = dict.fromkeys(range(10**6))" -- "list(d)" Python 3.5: Median +- std dev: 33.8 ms +- 0.7 ms Python 3.6: Median +- std dev: 37.8 ms +- 0.5 ms Seems this is compiler and platform specific, it is reproducible only with GCC on 32 bit. Proposed patch restores 3.5 performance and simplifies the code. Python 3.6 patched: Median +- std dev: 33.7 ms +- 0.7 ms Other types of iteration: $ ./python -m perf timeit -s "d = dict.fromkeys(range(10**6)); v = d.values()" -- "list(v)" Python 3.5: Median +- std dev: 26.2 ms +- 0.7 ms Python 3.6 unpatched: Median +- std dev: 28.0 ms +- 0.6 ms Python 3.6 patched: Median +- std dev: 26.3 ms +- 1.1 ms $ ./python -m perf timeit -s "d = dict.fromkeys(range(10**6)); v = d.items()" -- "list(v)" Python 3.5: Median +- std dev: 232 ms +- 6 ms Python 3.6 unpatched: Median +- std dev: 259 ms +- 6 ms Python 3.6 patched: Median +- std dev: 243 ms +- 9 ms _PyDict_Next(): $ ./python -m perf timeit -s "d = dict.fromkeys(range(10**6))" -- "set(d)" Python 3.5: Median +- std dev: 68.3 ms +- 1.8 ms Python 3.6 unpatched: Median +- std dev: 68.1 ms +- 2.5 ms Python 3.6 patched: Median +- std dev: 66.0 ms +- 1.2 ms PyDict_Next(): $ ./python -m perf timeit -s "from _testcapi import test_dict_iteration as t" -- "t()" Python 3.5: Median +- std dev: 3.31 ms +- 0.10 ms Python 3.6 unpatched: Median +- std dev: 3.51 ms +- 0.09 ms Python 3.6 patched: Median +- std dev: 3.43 ms +- 0.09 ms ---------- components: Interpreter Core files: dict_iter.patch keywords: patch messages: 276755 nosy: haypo, ned.deily, rhettinger, serhiy.storchaka priority: normal severity: normal status: open title: Clean up and speed up dict iteration type: performance versions: Python 3.6, Python 3.7 Added file: http://bugs.python.org/file44697/dict_iter.patch _______________________________________ Python tracker <rep...@bugs.python.org> <http://bugs.python.org/issue28183> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
