[Python-Dev] Making the __import__ hook available early...

[M.-A. Lemburg]

Tim Peters wrote:
> 
> [M.-A. Lemburg]
> > There has been some discussion on the import-sig about using
> > the __import__ hook for practically all imports, even early
> > in the startup phase. This allows import hooks to completely take
> > over the import mechanism even for the Python standard lib.
> >
> > Thomas Heller has provided a patch which I am currently checking.
> > Basically all C level imports using PyImport_ImportModule()
> > are then redirected to PyImport_Import() which uses the __import__
> > hook if available.
> >
> > My testing has so far not produced any strange effects. If anyone
> > objects to this change, please speak up. Else, I'll check it in
> > later today.
> 
> I don't understand the change, from the above.  Neither exactly what it does
> nor why it's being done.  So, impossible to say.  Was the patch posted to
> SourceForge?  Does it have a bad effect on startup time?  Is there any
> *conceivable* way in which it could change semantics?  Or, if not, what's
> the point?

I've already checked it in, but for completeness ;-) ...

The problem was that tools like Thomas Heller's pyexe, Gordon's 
installer and other similar tools which try to pack Python byte
code into a single archive need to provide an import hook which
then redirects imports to the archive.

This was already well possible for third-party code, but some
of the standard modules in the Python lib used 
PyImport_ImportModule() directly to import modules and this
prevented the inclusion of the referenced modules in the archive.

When no import hook is in place, the patch does not have any
effect -- semantics are the same as before. Import performance
for those few cases where PyImport_ImportModule() was used
will be a tad slower, but probably negligable due to the
overhead caused by the file IO.

With the hook in place, the patch now properly redirects these
low-level imports to the __import__ hook. Semantics will then
be those which the __import__ hook defines.

-- 
Marc-Andre Lemburg
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