You can dump the wallet only if it's not encrypted, what version of bictoin core do you run, make sure it's 17.1
PyWallet has a --passphrase option that will allow you to dump encrypted wallet.dat files... provided that you know the correct passphrase of course
You need to install python from python.org, then it should work
Also, you need to install Python 2.7.x... PyWallet will not work properly with Python 3