[Python-Dev] file (original) (raw)

Brett Cannon brett at python.org
Mon Mar 1 03:27:04 CET 2010

On Sun, Feb 28, 2010 at 12:46, Nick Coghlan <ncoghlan at gmail.com> wrote:

Brett Cannon wrote: > Actually it's four: name/init.py, name/init.pyc, name.py, and > then name.pyc. And just so people have terminology to go with all of > this, this search is what the finder does to say whether it can or > cannot handle the requested module.

Huh, I thought we checked for the directory first and only then checked for the init module within it (hence the generation of ImportWarning when we don't find init after finding a correctly named directory). So a normal miss (i.e. no directory) only needs one stat call. (However, I'll grant that I haven't looked at this particular chunk of code in a fairly long time, so I could easily be wrong). Robert raises a good point about the checks for extension modules as well - we should get an accurate count here so Barry's PEP can pitch the proportional reduction in stat calls accurately.

Here are the details (from Python/import.c:find_module) assuming that everything has failed to the point of trying for the implicit sys.path importers:

stat_info = stat(name) if stat_info.exists and stat_info.is_dir: if stat(name/init.py) || stat(name/init.pyc): load(name) else: for ext in ('.so', 'module.so', '.py', 'pyc'): # Windows has an extra check for .pyw files. if open(name + ext): load(name)

So there are a total of five to six depending on the OS (actually, VMS goes up to eight!) before a search path is considered not to contain a module.

And thanks to doing this I realized importlib is not stat'ing the directory first which should fail faster than checking for the init files every time.

-Brett

Cheers, Nick. -- Nick Coghlan | ncoghlan at gmail.com | Brisbane, Australia --------------------------------------------------------------- -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://mail.python.org/pipermail/python-dev/attachments/20100228/7c538a8f/attachment.html>

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