Hello!
Parselmouth abstracts this away, when reading (just like Praat itself, as Parselmouth mainly provides the Python interface). All audio files get read and immediately converted to 64-bit floating point numbers between -1 and 1.
If you need to know this information about the actual raw audio file, I think that your approach of using the built-in wave library seems correct. However, if the rest of your acoustic/phonetic/... analysis is done with Parselmouth, this info shouldn't matter too much?
Kind regards
Yannick