Some day, Linux distributions like Ubuntu are not going to package Python 2 even in a limited version, the way they're doing now. One way for us to deal with this would be to migrate all of our remaining little Python 2 programs and scripts to Python 3. Another option is to run them under PyPy , which says that it will always support Python 2.7 .

One of the potential issues with PyPy is that its JIT has a high warm-up cost , which means that small, short-running programs are going to be slower, perhaps significantly slower. Most of the Python 2 that we have left is in small administrative commands that are mostly run automatically, where on the one hand I would expect PyPy's overhead to be at its largest and on the other hand we probably don't really care about the overhead if it's not too big. So I decided to do some quick tests.

( I've been hit by the startup overhead of small programs in Python even without PyPy , but it was in an interactive situation.)

I did my tests on one of our Ubuntu 20.04 servers, which has PyPy version 7.3.1, and the results turned out to be more interesting than I expected. The artificial and irrelevant worst case was a Python 3 program that went from about 0.05 second to about 0.17 second (under pypy3) to actually do its work. Our typical small Python 2 commands seem to go from 0.01 or 0.02 second to about 0.07 second or so. The surprising best case was a central program used for managing our password file , where the runtime under PyPy actually dropped from around 0.40 second to 0.33 second. And a heavily multithreaded program that runs a lot of concurrent ssh commands had essentially the same runtime on a different 20.04 machine.

(In retrospect, the password file processing program does have to process several thousand lines of text, so perhaps I should not have been surprised that it's CPU-intensive enough for PyPy to speed it up. Somehow it's in my mind as a small, lightweight thing.)

All of this says that PyPy starts (and runs) our Python programs more than fast enough to serve us as an alternate implementation of Python 2 if we need to turn to it.