Upgrade Python version while running a Python program

Question

I would like to upgrade my Python version from 2.6.6 to the newest version of 3.6.5 on a server. However, there is a program that has been running for multiple days and will be running for a week or more.

Will my program continue to run until it finishes if I upgrade my Python version?

PS: I ran my Python program with the screen command so I wouldn't have to stop it to be able to upgrade my Python version.

Answer 1

Yes, your Python 2 script should continue to run while you install/upgrade Python 3, since Python 2 and 3 are different programs.
However, the installation will be be platform specific and there might be common dependencies, so I would test this on a different machine (eg local virtual machine) first.

Answer 2

Several aspects are to be considered here:

• In general, a Python program that is running does not access the installed binaries of the interpreter anymore. Also all the modules already loaded will not be read again from disk during the execution time of this program. (In this aspect it differs from eg a Bash script which reads its script source while executing.)
  So you probably are safe in even removing the complete Python installation; of course that's not what you plan on and I wouldn't recommend it for other reasons, but even that should not influence your running Python program.
  If, however, your running Python program tries to import a module for the first time after the removal or upgrade of your Python installation, this might fail due to incompatibilities between the versions. Most programs do their imports only at the beginning of their runtime, though.

• Python 2 and 3 are different languages. Scripts for the one need to be at least adjusted to run with the other. Adjustments aren't too hard to do, though. Most distributions have both installed side-by-side. Most of the time, Python2 is still standard (and accessed by typing python ). python2 and python3 are then to make it explicit.
  This means that you probably should not remove Python 2 from your system, even if you plan on installing Python 3. There probably are scripts relying on the installation of Python 2.

Answer 3

There's a lot going on here that you've not explained/described, so it's hard to give you a definitive answer (such as the operating system you're using). This is also not exactly a programming question, so you might find that the question gets voted to close. That said...

It possible to run multiple versions of Python side by side. Because 2.x and 3.x are very different, it might be much better to have both versions installed. See this answer for some details on doing that:

Official multiple Python versions on the same machine?

It's likely that your code will need some modifications to run on Python 3, so you're going to have to redeploy a new version of your code at some point anyway.