[Zope3-Users] Re: How to best include Zope3-based code in Zope3 unrelated Python projects?

[Philipp von Weitershausen]

Hermann Himmelbauer wrote:
> Hi,
> I have the problem that I cannot include parts of my Zope3 project in 
> external, Zope3-unrelated projects due to import errors.

You have problem and cause mixed up. You get import errors due to the 
fact that the Zope 3 libraries aren't on your PYTHONPATH.

> For instance, I currently build a LaTeX converter that automatically converts 
> SQL-Alchemy table definitions into nicely formatted LaTeX that I can then 
> include in my project documentation.
> 
> This converter has to import my table definitions file, which however fails, 
> as on the top of the file there are Zope3-specific imports and directives, 
> e.g.:
> 
> from zope.interface import implements
> import z3c.zalchemy
> metadata = z3c.zalchemy.metadata()
> 
> My Python interpreter does not know anything about zope yet, as it's not in 
> the PYTHONPATH, therefore the import of zope.interface fails. I assume, I 
> should somehow put the Zope3 modules into the PYTHONPATH - but how would you 
> recommend that? Should I perhaps link it from python/lib/site-packages? Or 
> should I include the Zope3 top-level directory into PYTHONPATH?

   $ export PYTHONPATH=/usr/local/Zope-3.3.x/lib/python
   $ python myscript.py

I would not recommend modifying the global Python installation to 
include Zope. For scripts, setting PYTHONPATH is simple enough. For 
anything fancier, I suggest using the setuptools mechanism to depend on 
the relevant Zope eggs (install_requires in setup.py) and installing it 
in a controlled environment (virtual-python, virtualenv or zc.buildout)

> Moreover, what's even more complicated is the import of z3c.zalchemy, how 
> should I solve that one?

   $ export 
PYTHONPATH=~/my/zope/instance/lib/python:/usr/local/Zope-3.3.x/lib/python
   $ python myscript.py

(assuming that z3c.zalchemy is installed as a package in your Zope 
instance).

> I thought about a construct like this:
> 
> if ???started via debugzope / zopectl???:
>    import z3c.zalchemy
>    metadata = MetaData()
> else:
>    from sqlalchemy import MetaData
>    metadata = MetaData()
> 
> But I don't know how to fomulate the if-clause above. Perhaps there's a better 
> solution to this problem?

   try:
       from z3c.zalchemy import MetaData
   except ImportError:
       from sqlalchemy import MetaData

   metadata = MetaData()


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