Comment 2 for bug 1935783

This type of error typically occurs because the cached .pyc files are out of date for some reason. (C.f. https://www.py4u.net/discuss/17141, https://stackoverflow.com/questions/30861493/how-to-fix-python-valueerrorbad-marshal-data)

This specific issue is occurring not in python-cryptography itself, but rather in the /usr/bin/py3compile call when its trying to import debpython. In other words, something's inconsistent with your system's cached python code. It sounds like perhaps force reinstalling python3-minimal might be worth trying.