[Python-Dev] Sharing expat instances

[Phillip J. Eby]

At 08:21 PM 12/14/2005 +0100, Fredrik Lundh wrote:
>Scott David Daniels wrote:
>
> > > > One good reason for this is that the .pyd's or .so's cannot necessarily
> > > > be used from zip files
> > >
> > > When you say "cannot necessarily", are the situations where they can be
> > > imported from zip files?  I thought the answer to that was always "no".
> >
> > I thought so too, but was not sure enough to state it that way.
>
>you could of course add them to the zip file, and automagically extract
>them before you start importing things.

The runtime system for Python Eggs does this; extraction is to a 
PYTHON_EGG_CACHE directory.  See e.g.:

    http://peak.telecommunity.com/DevCenter/PkgResources#resource-extraction

The egg builder writes a .py file alongside the .pyd or .so in the .egg 
file that contains something like:

    def __bootstrap__():
       global __bootstrap__, __loader__, __file__
       import sys, pkg_resources, imp
       __file__ = pkg_resources.resource_filename(__name__,'foobar.so')
       del __bootstrap__, __loader__
       imp.load_dynamic(__name__,__file__)

    __bootstrap__()

So, when you import from the zipfile, the .py file gets loaded (since 
zipimport doesn't support .pyd/.so/etc. imports directly) and then it 
reloads the module from the extracted file.  The other magic there is just 
to keep any of the special names from staying behind in the reloaded module.