https://player.backtracks.fm/talkpython/m/100-guido-van-rossum
Both audio and transcript. There is more discussion of Guido's pre-Python work than I have read before.
Discussion of Python 3 migration starts at 37:05. Guido says harder than expected because Python was more popular than he was aware of at the time.
-- Terry Jan Reedy -- https://mail.python.org/mailman/listinfo/python-list