default.nix

with import <nixpkgs> {};
with python27Packages;

stdenv.mkDerivation {
  name = "impurePythonEnv";

  src = null;

  buildInputs = [
    # these packages are required for virtualenv and pip to work:
    #
    python27Full
    python27Packages.virtualenv
    python27Packages.pip
    # the following packages are related to the dependencies of your python
    # project.
    # In this particular example the python modules listed in the
    # requirements.txt require the following packages to be installed locally
    # in order to compile any binary extensions they may require.
    #
    taglib
    openssl
    git
    libxml2
    libxslt
    libzip
    stdenv
    zlib
  ];

  shellHook = ''
    # set SOURCE_DATE_EPOCH so that we can use python wheels
    SOURCE_DATE_EPOCH=$(date +%s)
    virtualenv --no-setuptools venv
    export PATH=$PWD/venv/bin:$PATH
    pip install -r requirements.txt
  '';
}

nix-shell attempt

$ nix-shell
these paths will be fetched (0.03 MiB download, 0.16 MiB unpacked):
  /nix/store/2h5kilbwjpjs72w7k0y7j4b1yd343j6k-libxslt-1.1.33-py
copying path '/nix/store/2h5kilbwjpjs72w7k0y7j4b1yd343j6k-libxslt-1.1.33-py' from 'https://cache.nixos.org'...
New python executable in /home/aaron/codebases/solokeys/venv/bin/python2.7
Also creating executable in /home/aaron/codebases/solokeys/venv/bin/python
Installing pip, wheel...
done.
Traceback (most recent call last):
  File "/home/aaron/codebases/solokeys/venv/bin/pip", line 6, in <module>
    from pip._internal.main import main
ImportError: No module named main

[nix-shell:~/codebases/solokeys]$ 

requirements.txt

pandas