[Grok-dev] Re: First Experience with Grok

[Philipp von Weitershausen]

Martijn Faassen wrote:
>> I'd like to point out one issue I stumbled on at first.  After running
>> grokproject, the server would not start.  The exception I got was
>> cryptic.  After studying it, I realized my system had an older version
>> of zope.interface and Twisted installed in site-packages, and that the
>> sys.path constructed by grokproject preferred the version in
>> site-packages.  I fixed the problem by removing my site-packages path
>> from the generated runzope.  I suspect site-packages should never be
>> preferred over anything from the buildout-eggs directory.

Indeed. My suspicion is that Shane's running Ubuntu or Debian. Because 
those and other distributions install certain packages as development 
eggs into lib/python2.x/site-packages. I wish they wouldn't do that. For 
the problem is that buildout (through setuptools) will find them as 
regular eggs and put their "location" (which is site-packages) on 
sys.path. That's why Shane is getting site-packages *before* other eggs 
on sys.path.

> Unfortunately this problem occurs frequently. Many people also have Zope 
> 3 installed in their site packages, which leads to similar problems.

Those similar problems (No such module "schemaless") is actually a bug 
in zc.buildout: https://bugs.launchpad.net/zc.buildout/+bug/133462

> One way around this is to use an installation procedure in grokproject 
> that sets up a virtual Python environment. Ignas has contributed some 
> work in that direction.

Only problem with virtual-python (an the new virtualenv) is that they 
only work on Unix because they need symlinks.

> JW pointed the following out to me the other day, though: isolating 
> Grok's python from the system Python might make life harder for 
> beginners. If they install some useful Python package using easy_install 
> or, say, the Ubuntu package manager, they would expect it to be 
> available in their grok application and might be surprised if it's not. 
> The proper way to add dependencies would be to modify setup.py and/or 
> the buildout.cfg, but we may not want to confront beginners with a new 
> world of dependency management right away as well.
> 
> Perhaps we can resolve this by giving grokproject an option. By default, 
> it doesn't set up a virtual Python. However, if a certain option is 
> used, we do. We put in the instructions that if they have problems 
> installing or using Grok, they could try grokproject with the latter 
> option (and spell out the causes and consequences).

I think zc.buildout should gain such a feature proper: simply ignore 
anything installed anywhere other than your own eggs directory.


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