How can I change the default Python version on Snow Leopard?

"It’s easy:

defaults write com.apple.versioner.python Version 2.6

See man python for a complete explanation from Apple.

Also, one gotcha: make sure you are running the Python that came with your computer and not some other one that you installed. Do this by typing which python at your command prompt. It should point to /usr/bin/python. I only mention this because my default is 2.6 under Snow Leopard (it was 2.5 when I was using Leopard). So the fact that you are getting 2.5 may indicate that there’s something else in your path.

Update

To address comments below:

This doesn’t do what people are asking.

It does for me, in OS X 10.8.2. After doing defaults write com.apple.versioner.python Version 2.6, the default version of Python is indeed 2.6. (And likewise after changing back to 2.7.)

This is true whether I run python directly, or use an executable script starting with #!/usr/bin/env python—I get the expected version of Python.

This does not solve the symlink in /System/Library/Frameworks/Python.framework/Versions where Current point to 2.7 which may cause problems (because it is still in the sys.path with 2.6 !)

Indeed, it doesn’t fix that symlink.

However, run a short script that print()s the sys.path and (at least on my relatively default setup) the 2.6 library directories are on the path and the 2.7 dirs are not on the path. Nor is the Current symlinked directory on the path. So it should not be a problem for most scripts.

However, it’s possible—haven’t tested—that the Current symlink is used by either easy_install or pip. That would cause problems. It sure does seem like a bug that the symlink isn’t updated when you update the Python version."

"Assuming you're using bash, type:

% type -a python

That will show you all ""python"" executables, aliases, shell builtins (likely none) or bash functions in your PATH.

This should help you better identify what's going on here."