Sunday, September 16th, 2007

2 Python Environment Experiments

two experiments in the Python environment. The first is virtualenv, which is a rethinking of virtual-python.py, and my attempt to move away from workingenv. It works mostly like virtual-python.py, and on systems where it works (not Windows, nor Framework Mac Python) I think it works considerably better than workingenv. No more not a setuptools’ site.py, in particular. The basic technique is that it creates/copies a new python executable, and anything that uses that executable (including a script that references that executable with #!) will use that environment.

On the systems where it doesn’t work, I’m not quite sure what to do. The problem with the Mac is that sys.prefix is not determined by the location of the python executable, it’s hard-coded in some fashion. I asked about it on distutils-sig and got some response, but haven’t figured out any solution yet.

On Windows similarly sys.prefix is not determined by the executable location. What it’s determined by there I don’t know — the location of python25.dll, something in the registry? If I could figure it out, perhaps this could work there too — the existance of symlinks isn’t as important as it was with virtual-python.py.

If I can get these figured out, I think this will be a much happier experience than workingenv, and a somewhat friendlier experience than virtual-python.py. On non-Mac posix systems it works well right now.

The other experiment is in buildutils (downloadable with Mercurial): a new command python setup.py bundle, run in the application package you want to bundle. This creates a directory with all the dependencies of the application, and scripts that load up the appropriate dependencies. You can then ship the entire thing in a zip file as a runnable application that doesn’t require any installation except for unpacking.

Actually creating the bundle can be a little finicky, because easy_install has a tendency to prefer things on the local machine even though it shouldn’t. Probably it would be best to run this inside a virtualenv; when you are done you can also feel more confident that you’ve actually included all the dependencies (if you use —no-site-packages when creating the virtualenv).

Anyway, while both of these are a little incomplete I’m feeling optimistic about them, and I’m hoping intrepid souls can give feedback on how they work.

Update: virtualenv 0.8.2 is out, featuring Better Error Messages (and nothing else). Still doesn’t work on Mac Framework Pythons, or Windows. You’ll have to keep using workingenv there — but patches extremely welcome! Contact me if you are interested in supporting these platforms. It will involve some digging, but maybe we can just do the digging once for everyone.

Update 2: virtualenv 0.8.3 is out, featuring Windows!

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This is the personal site of Ian Bicking. It should (but I fear cannot) go without saying that the opinions expressed here are my own.