Python version hell

[John Ackermann N8UR]

I'm running Ubuntu 19.10 which installs Python 2.7 as the system
default.  I tend to use Python 3.7 for my projects, using a shebang line
of "#!/usr/bin/env python3".

When I first tried to build using scons on the cloned repo, it
complained because it couldn't find the pyserial module, which makes
sense because I installed that for python3.

After RTFM, I ran "scons target_python=python3.7" and that completed
without errors.

HOWEVER, the python programs like gpsrinex and gpsprof still use a
shebang line of "#!/usr/bin/env python" which executes the default
python2.7.

That of course fails, because the gps module is built for Python3 per
the target_python argument.

I don't know how the scons system works, but suggest that if a
target_python is specified, that version should be used in the shebang
line for the generated programs.

An additional related but minor point:

scons created /usr/local/lib/python3 and put the gps module there.
However, /usr/local/lib/python3.7 was already in existence and as noted
I had specified the python_target to be python3.7.

It seems a tad aggressive for scons to create a new version directory in
lib/ and particularly to do so with the major number when it's been
given both major and minor in target_python.

I think that on some Linux distros lib/python<major> is a symlink to
lib/python<major.minor>.  That doesn't seem to be the case on Ubuntu, at
least in /usr/local/lib.

Finally, guess what: in the newly released Ubuntu 20.04, the default is
now Python3! :-)


Thanks,
John