The implementation and hardcoded example is based on section 5.5 "HMM Part-of-Speech Tagging" in the Second Edition of Speech and Language Processing by Jurafsky & Martin (2009).
To run the script with the hardcoded example, simply run
python3 tagger.py
This will show the example observations (tokens) and states (POS tags)
['I', 'want', 'to', 'race']
['PPSS', 'VB', 'TO', 'VB']