[Python-ideas] disabling .pyc and .pyo files

Kevin Watters kevin.watters at gmail.com
Tue Dec 15 23:37:09 CET 2009

For what it's worth, I've got an entirely different use case than the 
ones I've seen in this thread so far.

I'd like Python to read .pyo files, but not search for .py or .pyc 
files. This is because we ship a py2exe app in it's "exploded" form, 
where there is an .exe and a lib/ folder full of .pyos.  Purely as an 
optimization, it'd be nice to not have Python stat for .py and then .pyc 
for every new import.

I remember glancing at Python/import.c and thinking that this could 
easily be accomplished by allowing the user to customize 
_PyImport_StandardFiletab at runtime--in fact there is already an 
PyImport_AppendInittab; it's just not exposed to Python. With a function 
like imp.set_inittab, I could get what I want with something like

     imp.set_inittab(['.pyo', 'rb', imp.PY_COMPILED])

And then of course to read just .py files, you could do

     imp.set_inittab([".py", "U", PY_SOURCE])

- Kevin

Kristján Valur Jónsson wrote:
> Hello there.
> We have a large project involving multiple perforce branches of hundreds 
> of .py files each.
> Although we employ our own import mechanism for the bulk of these files, 
> we do use the regular import mechanism for an essential core of them.
> Repeatedly we run into trouble because of stray .pyo (and/or .pyc) 
> files.  This can happen for a variety of reasons, but most often it 
> occurs when .py files are being removed, or moved in the hierarchy.  The 
> problem is that the application will happily load and import an orphaned 
> .pyo file, even though the .py file has gone or moved.
> I looked at the import code and I found that it is trivial to block the 
> reading and writing of .pyo files.  I am about to implement that patch 
> for our purposes, thus forcing recompilation of the .py files on each 
> run if so specified.   This will ensure that the application will 
> execute only the code represented by the checked-out .py files.  But it 
> occurred to me that this functionality might be of interest to other 
> people than just us.  I can imagine, for example, that buildbots running 
> the python regression testsuite might be running into problems with 
> stray .pyo files from time to time.
> Do you think that such a command line option would be useful for Python 
> at large?
> Cheers,
> Kristján
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