Python 2->3 was a poorly managed update that did not follow normal upgrade rules, so the "normal" rules don't apply.
It is still often very extremely expensive to convert python2 to python3. Normally you could upgrade in small steps, maybe a file or library at a time, instead of changing everything simultaneously including all transitive dependencies. That problem continues to be denied, so python2 continues to be used. I say that as someone who has converted code from 2 to 3. Python3 is fine, it's the huge unnecessary transition cost that is not. It's gotten a little better, but not a lot better.
This makes it worse. Now it's even harder to incrementally update, making it even harder to switch to 3.
Just some hack around that would probably already help.
I also supported things like obj.to_string("abc.gz") to get the record in gzip-compressed form.
I also had a from_string() -> obj functions.
You can see the problem. I had to change to_string() so it didn't allow compression (breaking backwards compatibility) and add a to_bytes() for that functionality, and add type dispatching in the from_string() code to support either byte or strings, with different code paths.
And change all the open() calls to use "b", and to add type checks on user-passed-in file objects to insist on reading bytes (if not isinstance(user_file.read(0), bytes) raise "Must be open in binary mode") because all of the underlying parsers are in C and the needless decode/encode step adds overhead.
Oh, and re-write the C extension so it handles both Python 2 and Python 3.
That was a really boring 6 weeks.
If of course you spent an extra decade producing obvious technical debt whose fault is it?
In many organizations there was never a time where they could start writing new code in Python 3. They needed to write code that was compatible with their existing python 2 code, and the only way to do that is to continue to write new code in python 2. Rinse, lather, repeat.
This is why the failure to provide a gradual transition was so bad. When I write new code in Python I use python3, but that assumes that there are python3 modules available that I need.
If you have infinite money this is not a problem. But I think we should be sympathetic to the people who do not have infinite money and have never been given a realistic upgrade path from 2 to 3. The 2to3 program is not a workable solution for many.
I joined an AI company on 2018 which was building their whole prototype with python 2.7 since 2017. I had to spend 2 weeks and do the migration myself, do a merge request out of the blue and give it to their lead engineers, otherwise i am pretty sure they would have a meeting tomorrow 24/1/2021 to see how they are going to migrate.
Just because industry has a habit of rewriting the whole stack every five years on account of make-work job security doesn't make foundational scientific algorithms change.
This was absolutely possible. Via the path of upgrading your code (or your dependencies code, in any arbitrary order) to be compatible with both py2 and py3 (via, say, six) and then once all code was compatible in either direction, flipping the switch.
I can think of exactly one language who bungled the upgrade path worse and it’s Perl 6, which they finally renamed after 19 years of stringing people along like it would be the next big thing.
