On Tue, Feb 7, 2012 at 16:51, PJ Eby <p...@telecommunity.com> wrote: > On Tue, Feb 7, 2012 at 3:07 PM, Brett Cannon <br...@python.org> wrote: > >> So, if there is going to be some baseline performance target I need to >> hit to make people happy I would prefer to know what that (real-world) >> benchmark is and what the performance target is going to be on a non-debug >> build. And if people are not worried about the performance then I'm happy >> with that as well. =) >> > > One thing I'm a bit worried about is repeated imports, especially ones > that are inside frequently-called functions. In today's versions of > Python, this is a performance win for "command-line tool platform" systems > like Mercurial and PEAK, where you want to delay importing as long as > possible, in case the code that needs the import is never called at all... > but, if it *is* used, you may still need to use it a lot of times. > > When writing that kind of code, I usually just unconditionally import > inside the function, because the C code check for an already-imported > module is faster than the Python "if" statement I'd have to clutter up my > otherwise-clean function with. > > So, in addition to the things other people have mentioned as performance > targets, I'd like to keep the slowdown factor low for this type of scenario > as well. Specifically, the slowdown shouldn't be so much as to motivate > lazy importers like Mercurial and PEAK to need to rewrite in-function > imports to do the already-imported check ourselves. ;-) > > (Disclaimer: I haven't actually seen Mercurial's delayed/dynamic import > code, so I can't say for 100% sure if they'd be affected the same way.) >
IOW you want the sys.modules case fast, which I will never be able to match compared to C code since that is pure execution with no I/O.
_______________________________________________ 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
