Developing and using the same Python on the same computer

Answer 1

You could set the PYTHONPATH as a global environment variable pointing to your Production code, and then in any shell in which you want to use the Development code, change the PYTHONPATH to point to that code.

(Is that too simplistic? Have I missed something?)

Answer 2

I'm guessing by virtual environment you mean the virtualenv package?

http://pypi.python.org/pypi/virtualenv

What I'd try (and apologies if I've not understood the question right) is:

• Keep the source somewhere that isn't referenced by PYTHONPATH (e.g. ~/projects/myproject)
• Write a simple setuptools or distutils script for installing it (see http://stackoverflow.com/questions/29562/python-distutils-does-anyone-know-how-to-use-it)
• Use the virtualenv package to create a dev virtual environment with the --no-site-packages option - this way your "dev" version won't see any packages installed in the default python installation.
• (Also make sure your PYTHONPATH doesn't have any of your source directories)

Then, for testing:

• Activate dev virtual environment
• Run install script, (usually something like python setup.py build install). Your package ends up in /path/to/dev_virtualenv/lib/python2.x/site-packages/
• Test, break, fix, repeat

And, for production:

• Make sure dev virtualenv isn't activated
• Run install script
• All good to go, the "dev" version is hidden away in a virtual environment that production can't see...
• ...And there's no (direct) messing around with PYTHONPATH

That said, I write this with the confidence of someone who's not actually tried setting using virtualenv in anger and the hope I've vaguely understood your question... ;)

Answer 3

You can add/modify python paths at sys.path, just make sure that the first path is the current directory ".", because some third-party modules rely on importing from the directory of the current module.

More information on python paths: http://djangotricks.blogspot.com/2008/09/note-on-python-paths.html