Zato blog post: A successful Python 3 migration story

Terry Reedy tjreedy at
Mon Feb 11 13:18:34 EST 2019

The migration was from 2.7 to 2.7 and 3.x, rather than 3.x only.
I think it worth reading for anyone interested in the subject.

60,000 lines of Python and Cython, 130 external dependencies (but only 
10 not already 3.x ready) took 2 people 80 hours total.

Their head start was to write the 2.7 modules, from the beginning, with 
the following at the top.
from __future__ import absolute_import, division, print_function, 

Terry Jan Reedy

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