Python discussion

python basics

• *.pth files

Python supports *.pth files which contain the paths to the parent directories of your python modules one per line. Those files are placed in site-packages and are typically generated by python package managers such as easy_install.

• PYTHONPATH

The other way is to set additional paths for the required modules before running python. This is done by setting the python paths in the environment variable PYTHONPATH. A path typcially looks like this on a Nix system: /nix/store/fxpfc2hyw5qbxly8xwrxzai8lny4pcq2-ipython-0.11/lib/python2.7/site-packages/ipython-0.11-py2.7.egg

• PYTHONUSERBASE

?

in general see [1]

general python integration into nixos

requirements

• mix python 2.x and 3.x in the same profile

marcweber and qknight vote against that. it makes packaging complicated: to mix python2 and python3? We could introduce NIX_PYTHON_SITES_2 and NIX_PYTHON_SITES_3 or such. a better way is to use load-env-whatever (see [2] )

• pyLibA (python wrapper for a library) is used by pyLibB: nix expressions must be able to use either

proposed nixos environment variables

• NIX_PYTHON_SITES

qknight's problems

packaging virt-manager

see problem 2 in [3]

python-gudev

i have problems packaging python-gudev:

 gudevmodule.c:19:23: fatal error: pygobject.h: No such file or directory

but looking at the exports (nix-env -i python-gudev -K; source env-vars) i can see:

-I/nix/store/lqsihhkhl7rhr18x7qiviihyp2byc5gw-pygobject-2.27.0/include

but in that folder there is only pygtk-2.0 folder:

 ls -la /nix/store/lqsihhkhl7rhr18x7qiviihyp2byc5gw-pygobject-2.27.0/include
 pygtk-2.0/

so in that folder i find:

 ls -la /nix/store/lqsihhkhl7rhr18x7qiviihyp2byc5gw-pygobject-2.27.0/include/pygtk-2.0/
 pyglib.h  pygobject.h

the problem

as discussed in [4] and quoting [5]

   # All python code is installed into a "gtk-2.0" sub-directory. That
   # sub-directory may be useful on systems which share several library
   # versions in the same prefix, i.e. /usr/local, but on Nix that directory
   # is useless. Furthermore, its existence makes it very hard to guess a
   # proper $PYTHONPATH that allows "import gtk" to succeed.

so how should i package python-gudev then? the source for python-gudev (which produces the above error) can be found at [6]