FWIW, which might not be much, and this isn't enforced across the codebase... but I try to, when possible, group imports by Group 1) 'standard lib', Group 2) '3rd party libs', Group 3) 'zipline libs'.

Though that could stand both/either, rethinking, or making more explicitly documented in a style guide.

i.e. that `sys` was import intentionally ordered before the `six` import.