On 29 November 2016 at 03:28, Guido van Rossum <gu...@python.org> wrote: > On Mon, Nov 28, 2016 at 9:14 AM, Nathaniel Smith <n...@pobox.com> wrote: >> >> Also note that in Guido's option 2, we only incur the extra fstat calls if >> the import would otherwise fail. In option 1, there are extra fstat calls >> (and thus disk seeks etc.) adding some overhead to every import. > > Oh, that's an important consideration! Yes, adding .missing.py to the list > of extensions would cause extra stat() calls and potentially slow down every > import.
This is the second time I've seen "but stat calls!" concern in relation to import today, so I'll echo what Brett pointed out in his reply: the import system in recent 3.x releases, along with the importlib2 backport to Python 2.7, builds a cache of the directory contents for path entries rather than making multiple stat calls. The current 3.x source code for that is at https://hg.python.org/cpython/file/tip/Lib/importlib/_bootstrap_external.py#l1280 The significant reduction in the number of stat calls through better caching is the main way the 3.3 import reimplementation in Python managed to be competitive performance-wise with the previous C implementation, and faster when importing from a network filesystem :) Cheers, Nick. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
