[Distutils] patches: ez_setup.py: don't import setuptools into your current address space in order to learn its version number

[Phillip J. Eby]

At 04:36 PM 10/2/2007 -0600, zooko wrote:
> > Okay.  Attached is a patch that doesn't import pkg_resources and
> > doesn't reload anything.  I haven't yet tested it -- I am
> > submitting it only to inform the discussion and get any early
> > feedback from you on whether the very idea is sound.
>
>Okay, I tested this patch on Mac OS X and it worked.  First I
>installed setuptools v0.6c3, then I tried to execute allmydata.org 's
>"setup.py install".  I got the error message saying that it couldn't
>install a newer version of setuptools (v0.6c7) when an older version
>was already loaded.  Then I applied my patch to ez_setup.py and tried
>again.  This time it installed v0.6c7.

Interesting.  But the patch doesn't actually address the real issue 
with importing; i.e., upgrading setuptools in-place *while setuptools 
is already running*.

In other words, the test I care about is what happens when you run 
easy_install on the package, not "setup.py install".

Or, to put it more succinctly:

     if 'pkg_resources' in sys.modules or 'setuptools' in sys.modules:
         # setuptools is installed, but can't be upgraded, so
         # just version check (using pkg_resources) and exit if
         # it's not a good enough version.
     else:
         # okay to import pkg_resources and check for version,
         # as long as afterwards we del sys.modules['pkg_resources']
         # and re-import it.

So the subprocess and the duplication of code from pkg_resources is 
unnecessary, since it does not fix the problem when the code is run 
via easy_install.