Hi,
I'm trying to create a Nix package for this python application:
https://github.com/spl0k/supysonic
I used `buildPythonApplication` from `nixpkgs` and I can correctly install the application and run the files in `$out/bin`, the problem is that I also need a file, called `server.py` that is in the repository but it's not installed with `setup.py`. So I added a `postInstall` phase that copy `server.py `in `$out/bin`, nix automatically wraps this file but when I try to execute it I receive the following error:
```
File "/nix/store/p9qn5qiqf0mwpcb7zfwyq3d1r6v1wqm5-supysonic/bin/server.py", line 2
    export PATH='/nix/store/lm0w36273v76nnph1518gwbv1g45sl8w-python3-3.7.7/bin:/nix/store/p9qn5qiqf0mwpcb7zfwyq3d1r6v1wqm5-supysonic/bin:/nix/store/00iijl9s12z2qy8gjggdn72d3l3vipbi-python3.7-setuptools-45.2.0/bin:/nix/store/l0k7bm0kah5q1divcnwrrhm1di5b1bzk-python3.7-Flask-1.1.1/bin:/nix/store/2qkzrbfrq72nx5mphizsx7xwvvgy395p-python3.7-mutagen-1.43.0/bin:/nix/store/6s30qmbz43wfph1qwb6q95bh4g7i5pg8-python3.7-watchdog-0.9.0/bin:/nix/store/7bxj2sa1bzj33s880bml0s29kp2ykpcm-python3.7-chardet-3.0.4/bin'${PATH:+':'}$PATH
              ^
SyntaxError: invalid syntax
```
Which is a python error, and before that error some Python code is executed because it produces some output. Any ideas? I'm a noob with Nix and Nixos. Thank you!