In their discussion of 'List replication operator' Steven D'Aprano and Ben Finney used these '_' and '__'. Steve said, "[[] for _ in range(5)]". Ben said, "[ [] for __ in range(5) ]".
These aren't listed separately in the index, where might I find written discussion of these? Thanks, Mike -- "There are three kinds of men. The ones who learn by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves." --- Will Rogers -- https://mail.python.org/mailman/listinfo/python-list