I'm not a Python developer but what I've seen and find frustrating is the slow migration of libraries to Python 3. Some projects have switched to 3 and some are sticking with 2 for now. Some applications are using 2 because they have dependencies using 2, but as those dependencies switch applications have to deal with combining Python 2 and Python 3 dependencies.

I know each issue is easy in isolation, but we're talking about old 25M line codebases here. If such things exist in Python it can be a maintenance problem.

I'm in favor of languages making breaking changes occasionally but there is something to be said for languages like Java or Fortran that are intended to keep compatibility forever.