[Python-Dev] PEP 3147, cached, and PyImport_ExecCodeModuleEx() (original) (raw)

Guido van Rossum guido at python.org
Fri Apr 9 23:52:16 CEST 2010

It may be undocumented but it doesn't start with _ and it exists to preserve backwards compatibility. So I recommend adding PyImport_ExecCodeModuleExEx().

On Fri, Apr 9, 2010 at 1:24 PM, Barry Warsaw <barry at python.org> wrote:

I've run into a minor snag implementing the cached attribute on imported modules.  From PEP 3147:

 As part of this PEP, we will add an _cached_ attribute to modules,  which will always point to the actual pyc file that was read or  written.  When the environment variable $PYTHONDONTWRITEBYTECODE is  set, or the -B option is given, or if the source lives on a  read-only filesystem, then the _cached_ attribute will point to  the location that the pyc file would have been written to if it  didn't exist.  This location of course includes the _pycache_  subdirectory in its path. The right place to add this seems to be PyImportExecCodeModuleEx(), which passes in a pathname argument.  This function is not documented in the C API reference manual and about the only place where it's described is Misc/HISTORY:  - New function PyImportExecCodeModuleEx(), which extends  PyImportExecCodeModule() by adding an extra parameter to pass it the  true file. The "true file" can either be the source .py file, the legacy .pyc file, or the PEP 3147 .pyc file depending on the circumstances.  The caller knows which it is, but that function itself doesn't.  I've tentatively worked out some code that lets it guess, but it's a kludge, it's ugly and I don't like it.  I think the right fix is to extend PyImportExecCodeModuleEx() to also pass in the pathname for cached (or NULL if None is appropriate). It bothers me a little to change this API, but OTOH, it's an undocumented API, so I don't feel too badly. ;) Since this is one of the last things to implement for PEP 3147, I thought I'd ask and see if anybody had any better suggestions. -Barry

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-- --Guido van Rossum (python.org/~guido)

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