Fabrice,

> Maybe it would be better if eups always run with system python ?

	In the not-too-distant future (maybe even in January or
February), I think we want to convert the LSST Stack to run with the
system Python in all cases, including eups.

> Indeed for now it switch to eups-installed python once command
> "setup python" is performed.

	"setup python" would go away.  But I'm not sure what the problem
is with switching Pythons.

> >	Regarding its use with virtualenv, EUPS has been designed with
> >virtual-env like functionality in mind -- specifically, it manages the
> >PYTHON_PATH for you. So using the two together is likely to generate
> >conflicts (though it may not be impossible).

> One of the main advantage of using virtualenv is that install of
> python libraries via eups is completely transparent : you don't have
> to manage a dedicated PYTHONPATH in eups build scripts of python
> libraries.
> It also isolate eups-installed python and then prevent conflicts
> between system python user libraries and eups-installed python user
> libraries.
> Of course, if you prefer, i can set up build script to install each
> Qserv python lib in a dedicated directory and then add it to
> PYTHONPATH.

	We already have the PYTHONPATH manipulation in the rest of the
LSST Stack, so I think it's best for now to continue with that.  In the
longer run, I would like to see all LSST Stack Python modules installed
into a single directory, almost certainly an LSST-specific one and not
the system site-packages -- but they would be swapped in and out on
setup of the individual packages through the use of symbolic links.

	One of the main reasons to use the system Python is to allow the
user to incorporate other packages into their usage of the LSST Stack.
virtualenv does not work well with this usage model.  This may not be an
issue with qserv, however, which is server-side and can insist on a more
rigorously-controlled environment.

-- 
Kian-Tat Lim, LSST Data Management, [log in to unmask]

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