My question is do you want to learn the exact bass lines of Penny Lane, or any other song, or do you want something that is close?

If you want to the exact line then Backingtracks first paragraph is what I would have said also. Adding to it you might want to purchase a transcribed MIDI Penny Lane song. Just be sure to listen to the MP3 of the transcribed MIDI song so you can determine if it is a true transcription. You could also bring the MIDI file into either BiaB or your DAW for practicing the bass lines.

If you want get to something close you can put the chords into BiaB, mute the bass line, and practice your bass.

Either way make sure you are having fun.

Whenever I get something stuck in the back of my throat, I dislodge it by drinking a beer.
It's called the Heineken Maneuver.

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware