Bite of the Buildbugs!

[Richard Laager]

On 12/11/2017 07:45 PM, Gary E. Miller via devel wrote:> Binary distro
installs, unexpectedly to some, go into a temporary> location
(/var/tmp/XX?).
Not that it matters much, but just for clarification... For Debian, the
temp location is ./debian/tmp (where . is the source tree). For RedHat,
it often was /usr/src back in the day; otherwise maybe ~/.rpmbuild. It's
been quite a while since I've done RPM packaging.

> I missed a lot of the PYTHONPATH, sys.path and .pth
> discussion.  Can someone(s) post quick compare and contrast of these
> three ways to proceed?
sys.path is the path that is actually searched. sys.path is built from a
set of installation-dependent defaults, plus the value of the PYTHONPATH
environment variable. That is, PYTHONPATH is *added* to the default
sys.path. Contrast this with PATH, where the environment variable *is*
the list to be searched.

For example, try these on your system:

$ python -c 'import sys; print sys.path'

$ PYTHONPATH=/opt/foo/site-packages \
  python -c 'import sys; print sys.path'

You will see that PYTHONPATH *adds* to sys.path. Paths in PYTHONPATH are
added high in the list (second, after '' which is the current
directory), so paths in PYTHONPATH are searched before the
installation-dependent defaults.

.pth files are another way to *add* to sys.path.

If your Python is missing /usr/local/.../site-packages option(s), you
have two ways to add them: PYTHONPATH or a .pth file (in
/usr/lib/pythonX.Y). I believe that a .pth file is generally preferable
to setting PYTHONPATH, as it is often challenging to ensure that
environment variables are set/inherited everywhere you need. For
example, cron, systemd units, and sudo tend to have separate environments.

-- 
Richard

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