For example, #fdroidserver is coded against apksigner from build-tools version vX.0.0. Someone does `pip install fdroidserver`. Then at some point, the user upgrades apksigner to version vY.0.0 which breaks the parsing before fdroidserver supports apksigner vY.0.0. That breakage needs to fail gracefully, and that is really hard to do. Much harder than just writing pure Python code to extract the certificates which is tested against the apksigner test suite. 2/3