This is meant to create a compilation of packages to be updated for nixpkgs-update.
# collect updates for python-modules
./main.py pkgs/development/python-modules/*/default.nix > $XDG_CONFIG_HOME/package-to-update.txt
or
# update all non-frozen packages that use buildPython{Application,Package}
grep -rl ./nixpkgs -e buildPython | grep default | ./main.py > $XDG_CONFIG_HOME/package-to-update.txt
Thanks to @fridh who created the original script located: https://github.com/NixOS/nixpkgs/blob/master/pkgs/development/interpreters/python/update-python-libraries/update-python-libraries.py