[Distutils] patch: solving the two major things that people dislike about setuptools, part 1

[Mark Sienkiewicz]

zooko wrote:
> Folks:
>
> There are two things that cause a lot of people to object to the use
> of setuptools: that it changes the semantics of PYTHONPATH, making it
> impossible to override packages on the command-line, and that it
> doesn't work when you run "setup.py install --prefix=./some_dir".

This is #1 on my list of why I hate setuptools.  I actually had it 
installed (we were wondering if we should distribute our software with 
setuptools), but I removed it when I found out that it broke PYTHONPATH.

I have a question about this patch, though:

It is somewhat awkward to apply your patch because setuptools is 
distributed and installed as a .egg file.  Rather than trying to figure 
out how to apply a patch inside a .egg file, I tried to see what the 
effect on easy_install.pth would be.  I changed my easy_install.pth file 
to look like this:

import sys; sys.__plen = len(sys.path)
import sys; print "egg insert at",sys.__egginsert
./nose-0.10.4-py2.5.egg
import sys; new=sys.path[sys.__plen:]; del sys.path[sys.__plen:]; 
p=getattr(sys,'__egginsert',len(os.environ.get('PYTHONPATH','').split(os.pathsep))); 
sys.path[p:p]=new; sys.__egginsert = p+len(new)


I think that this is what your patch would do, except for the debugging.

In my testing, I found that this easy_install.pth file behaves exactly 
the same as the old one.  That is because sys.__egginsert exists and is 
always 0; the value you get from looking at the environment is never 
used.  You can verify this from the print statement I included in the 
.pth file:

[banana:~] sienkiew% python
egg insert at 0
Python 2.5.1 (r251:54863, Mar 18 2008, 11:29:59)
[GCC 4.0.1 (Apple Computer, Inc. build 5367)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
 >>> import setuptools ; setuptools.__version__
'0.6c9'


Have I understood your patch correctly?  Do you have different behaviour 
on your system?

I think the correct behaviour is to insert the .egg file either just 
before or just after the directory where we found the .pth file.

So, instead of
p=getattr(sys,'__egginsert',len(os.environ.get('PYTHONPATH','').split(os.pathsep))); 


we want
p=sys.path.index(sitedir);

We can eliminate __egginsert from the code entirely.  As far as I can 
tell, the *only* purpose of __egginsert is to permit the incorrect 
behaviour that your patch is intended to fix.

Does that make sense to you?

Mark S.