NOTE: Type names and effectiveness extracted from https://github.com/pret/pokeemerald project source code
Windows:
py ./pokemon.py [pokemon]
Linux/Unix/Mac:
python3 ./pokemon.py [pokemon]
Or (make sure script is executable and check the shebang line):
./pokemon.py [pokemon]
If you don't supply the name of a pokémon, it will prompt you for one.