Hi,

Python 2 reached EOL about a year ago thus the 'python' command may be
missing on some systems.
'python3' is the standard way of invoking the Python 3 interpreter,
thus Emacs would have a better chance trying that.

The attached patch is already carried in Ubuntu.

Cheers,
Balint

[1] https://www.python.org/doc/sunset-python-2/

-- 
Balint Reczey
Ubuntu & Debian Developer