The Python interpreter on webOS 1‒6 is python (Python 2.7), while on webOS 7+ it's python3.
To make a Python script that can be run on any version of webOS, I added a bit of shell script at the top that figures out the name of the Python interpreter and uses that to re-execute itself:
#!/bin/sh
''''command -v -- python3 >/dev/null && exec python3 -- "$0" "$@" || exec python -- "$0" "$@" # '''Python ignores this because it just sees a docstring (idea from here), and the shell is no longer running after exec. I'm sure someone else has already done this, but I didn't really know what to search for. (Edit: Found this. It's more thorough, but a lot longer.)
Example (test.py):
#!/bin/sh
''''command -v -- python3 >/dev/null && exec python3 -- "$0" "$@" || exec python -- "$0" "$@" # '''
print("hi")
import sys
print(sys.argv)$ ./test.py -a -b -c 123 'asdf qwer'
hi
['./test.py', '-a', '-b', '-c', '123', 'asdf qwer']
Of course, the Python code itself has to be compatible with Python 2 and 3.
I've tested this with ash from BusyBox v1.29.3 (webOS 6) and v1.31.1 (webOS 8) as well as Bash 5.2.15.