Our real problem with a removal of Python 2 is likely to be our users
In my recent entry on whether Ubuntu 20.04 LTS will include Python 2, I mentioned that this mattered because we have various system management tools written in Python 2, so if Python 2 was not going to be in 20.04, we'd need to start porting them so they'd be ready in time. Unfortunately, this need to port our system tools is probably not going to be the most painful part of the day that Ubuntu ships without Python 2. Instead, the real problem is our users. More specifically, the problem is all of the Python (2) programs that our users will have written over the years and still use and need.
Well, let me rephrase that. I shouldn't say 'users'; I should say 'the graduate students and professors of the department' (and also researchers, postdocs, undergrads doing research work with professors, visiting collaborators, and so on). Unusually for the modern world, we provide general multiuser computing to all of these people, and so these people log on to those Ubuntu-based servers and do whatever they want (more or less) with the things that Ubuntu provides. Some of these people write Python programs, and some of them are probably Python 2 programs. When Python 2 goes away, those programs are going to break.
(They will also probably break if
/usr/bin/python turns into
Python 3, which is one reason I hope Ubuntu doesn't do that any
time soon. There being no
/usr/bin/python is less confusing and
easier to explain to angry users than '
python is now incompatible
with what it was a week ago, sorry about that'.)
A few of these people are probably avid Python users and already know about Python 3. Of course, these people are probably already writing everything in Python 3, so they're unaffected by this. Many more of these people probably don't know about Python 3 for various reasons, including that their real work is writing a thesis or doing research, not knowing about developments in the programming language that they're working in. To add to the difficulty, we don't even know who they are (and I'm not sure how we'd find out, unless there is some very lightweight and non-intrusive way of instrumenting our systems to gather data when Python 2 gets run).
(Since we can't currently give our users any definitive information on when they won't have Python 2, it's also not very useful to reach out to them right now. Many of our users would rightfully consider rewriting things from Python 2 to Python 3 to be a distraction from their thesis or their research, and for that matter they may only need their Python 2 programs for a relatively limited time.)
The basically inevitable result of this is that we're likely to be forced to install Python 2 for backward compatibility for at least one LTS generation after Ubuntu drops it officially. Hopefully there will be people packaging Python 2.x as a PPA, which is the most convenient option on Ubuntu. The possible exception for this would be if Ubuntu gave everyone a significant amount of advance warning, for example if they announced before 20.04 that it would be the last release that included any version of Python 2 in the normal Ubuntu repositories. Then we could at least start trying to reach users, not that I expect us to be very successful at it.
PS: We're definitely not going to ever change
print a warning about the situation (for many reasons including
that warnings are often fatal errors in practice), and I'm pretty sure we'd never alter
it to syslog things when it starts. Any method of acquiring information
about when Python 2 gets run needs to be entirely external.