[Nix-dev] Re: Python 3

[Peter Simons]

Hi Marc,

 >> Can your new-and-improved python expression support [install Python
 >> 2.5 and 3.0.1 simultaneously]?
 >
 > How should it look like? I mean you can install to different profiles
 > and you're fine.

Yes, I know, but how does your expression support installing different
versions of Python? I don't want to copy the entire expression and
rename all occurrences of the string "2.5" with "3.0", right?
Expressions are functions, so clearly there has to be better way
duplicating the entire thing whenever a parameter changes.


 >> What do you mean by "fix"? What is broken about the current default
 >> expression?
 >
 > One major problem is that a lot of python libraries check for its
 > dependencies. Only using PYTHONPATH isn't nough in most cases, cause
 > the import directories do cantain .pth files or such listing more
 > directories to be added to the import path.

We have talked about this particular subject before:

  http://article.gmane.org/gmane.linux.distributions.nixos/1430
  http://article.gmane.org/gmane.linux.distributions.nixos/1447

The second article lists several approaches how to remedy the problems
you refer to. Have you seen that article when I posted it back then? I
wonder, because you never responded to it, so maybe it got lost in
transmission somewhere.

It would be really nice if we could find a good solution to this
problem, because there are lots of packages that suffer from it (ghc,
tex, ruby, etc.), not just Python.

Take care,
Peter