Years ago Debian created /usr/local/lib/pythonVERSION/site-packages,
and compiled the Python binary to include it in the default search
path. Ubuntu followed Debian's lead as it normally does. The Python
developers did not like this because you'd get interference with a
locally-installed /usr/local/bin/python using the same site-packages
directory. Ubuntu finally decided to abandon site-packages and use
dist-packages instead, a name which they invented so it wouldn't
interfere with anything. The loing story is out there somewhere if
you google it, somewhere in the Python bug tracker or distutils SIG or
such.
The system works, at least if you use the Ubuntu virtualenv package.
Some people have had problems using a locally-installed virtualenv on
Ubuntu because the magic sys.path entries weren't being added or
something. I'm not sure about --no-site-packages because I never use
that option: I run PIL and mysqldb from the Ubuntu packages because it
can be hard to compile their C dependencies sometimes. (Need the
right header files, Python is ignoring the header files, etc.)
So Ubuntu Python packages go into
/usr/lib/pythonVERSION/dist-packages. Or that python-support
directory for some reason. Locally-installed Python packages go into
/usr/local/lib/pythonVERSION/dist-packages by default. Whenever I
install an Ubuntu 9.04 system I run:
$ sudo apt-get install python-setuptools (6.0c9)
$ sudo apt-get install python-virtualenv (1.3.3)
$ sudo easy_install pip
$ sudo pip install virtualenvwrapper
The virtualenvs work fine this way, although I haven't tried --no-site-packages.
> I'm trying to spin up virtualenv, and the --no-site-packages flag
> seems to do nothing with ubuntu. I installed virtualenv 1.3.3 with
> easy_install (which I've upgraded to setuptools 0.6c9)
yourself by installing them locally.
> and everything
> seems to be installed to /usr/local/lib/python2.6/dist-packages
Yes
> I assume that when installing a package using apt-get, it's placed in /
> usr/lib/python2.6/dist-packages/ ?
Yes
> 4. Is it first come first serve on the path? If I have a newer
> version of package XYZ installed in /usr/local/lib/python2.6/dist-
> packages/ and and older one (from ubuntu repos/apt-get) in /usr/lib/
> python2.6/dist-packages, which one gets imported when I import xyz?
> I'm assuming this is based on the path list, yes?
sys.path is scanned in order. The only funny thing is that .pth eggs
get put earlier or later in the path than some people expect. But if
you're using pip for everything it can do (i.e. except to install pip
itself, precompiled eggs, and a snapshot of a local directory that's a
copy rather than an egg link), you won't have many .pth eggs anyway.
> 5. Why the hell is this so confusing? Is there something I'm
> missing here?
It's not well documented. I figured it out by scanning the web.
> 7. Will this affect pip as well?
Yes, pip will automatically install to
/usr/local/lib/pythonVERSION/site-packages. Use "pip install -E
$VIRTUAL_ENV packagename" to install into a virtualenv.
--
Mike Orr <sluggos...@gmail.com>
