> Are there some valid reasons that made 2->3 migration insanely hard for some projects?
Print was a non-issue once you could do "from __future__ import print_function". It was the unicode migration.
All string handling from I/O required at least checking.
The dependency issue was the most crippling, though: because you can't load Python 2 code from Python 3, before your project can begin migrating you have to wait for all your dependencies to update as well. This may involve them changing the types that get passed over the API from 'str' to 'bytes' or vice versa, which is potentially a breaking change.
Print was a non-issue once you could do "from __future__ import print_function". It was the unicode migration.
All string handling from I/O required at least checking.
The dependency issue was the most crippling, though: because you can't load Python 2 code from Python 3, before your project can begin migrating you have to wait for all your dependencies to update as well. This may involve them changing the types that get passed over the API from 'str' to 'bytes' or vice versa, which is potentially a breaking change.