On Mon, Mar 1, 2010 at 08:30, Ron Adam <r...@ronadam.com> wrote: > > > Nick Coghlan wrote: > >> Michael Foord wrote: >> >>> Can't it look for a .py file in the source directory first (1st stat)? >>>> When it's there check for the .pyc in the cache directory (2nd stat, >>>> magic number encoded in filename), if it's not check for .pyc in the >>>> source directory (2nd stat + read for magic number check). Or am I >>>> missing a subtlety? >>>> >>> The problem is doing this little dance for every path on sys.path. >>> >> >> To unpack this a little bit for those not quite as familiar with the >> import system (and to make it clear for my own benefit!): for a >> top-level module/package, each path on sys.path needs to be eliminated >> as a possible location before the interpreter can move on to check the >> next path in the list. >> >> So the important number is the number of stat calls on a "miss" (i.e. >> when the requested module/package is not present in a directory). >> Currently, with builtin support for bytecode only files, there are 3 >> checks (package directory, py source file, pyc/pyo bytecode file) to be >> made for each path entry. >> >> The PEP proposes to reduce that to only two in the case of a miss, by >> checking for the cached pyc only if the source file is present (there >> would still be three checks for a "hit", but that only happens at most >> once per module lookup). >> >> While the PEP is right in saying that a bytecode-only import hook could >> be added, I believe it would actually be a little tricky to write one >> that didn't severely degrade the performance of either normal imports or >> bytecode-only imports. Keeping it in the core import, but turning it off >> by default seems much less likely to have unintended performance >> consequences when it is switched back on. >> >> Another option is to remove bytecode-only support from the default >> filesystem importer, but keep it for zipimport (since the stat call >> savings don't apply in the latter case). >> > > What if ... a bytecode-only mode is triggered by "__main__" loading from a > bytecode file, otherwise the .py files are needed and are checked to make > sure the bytecode files are current. > > That's way too magical for my tastes, especially if you mess up and accidentally leave behind a __main__.pyc after moving the __main__.py file.
-Brett > Ron > > > > > > > _______________________________________________ > 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/brett%40python.org >
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