[Python-Dev] Zip import and sys.path manipulation (was Re: directory hierarchy proposal)

[Phillip J. Eby]

(CC'd to python-dev because of possible impact on zipimport implementation/API)

At 08:00 AM 12/16/02 -0500, Jim Fulton wrote:
>Each zope package __init__ file would have a bit of boilerplate code
>that would include all zope directories in sys.path:
>
>   # Boilerplate code that combines all zope directories in sys.path
>   import sys, os
>   __path__ = [os.path.join(p, 'zope') for p in sys.path]
>
>Jim

That should probably read:

__path__ = [os.path.join(p, 'zope') for p in sys.path if 
isinstance(p,StringTypes)]

or else it could break in 2.3 if somebody's putting non-strings on 
sys.path.  I don't remember exactly how the python-dev discussion turned 
out, but I kind of got the impression that it was going to be allowable in 
2.3.  Also, I'm pretty sure it will not give the expected/desired results 
in conjunction with zipfile imports.

For these and related reasons, I would suggest that a slightly different 
snippet be used instead (the names are lousy, improvements welcome):

from namespace_packages import makeNamespacePath
__path__ = makeNamespacePath('zope')

And then make whatever carries "namespace_packages" be something that's 
distributed separately from Zope, preferably part of the standard library 
or distutils (and backported where possible).       If we can make it so 
that the __init__ code never *has* to change, that will minimize the 
likelihood of incompatible __init__.py's floating around.  Meanwhile, a 
module that actually *knows* something about what can be on sys.path (and 
how to interpret it) can do so.

In order to support something like this, importer objects would need to be 
able to return something that's the moral equivalent of "os.path.join" on 
an existing sys.path entry; either another importer object or a string that 
can be handled by one.  At this point, checking for a '.zip' extension at 
the end of a string isn't going to cut it any more.