Briefly, the issue is that when installing psycopg2 in a
virtualenv that was created with --no-site-packages
(in an attempt to be completely independent of the underlying
system), psycopg2's setup.py will still find mx and set
HAVE_MXDATETIME=1. The compilation and install
succeed, but since mx isn't installed in the virtualenv, importing
psycopg2 results in an ImportError: can't import mx.DateTime
module.
As far as I can tell, this happens because setup.py does
mxincludedir = os.path.join(get_python_inc(plat_specific=1), "mx")
to determine whether mx is available. That will find the mx
include directory (eg, /usr/include/python2.6/mx) and
it will be able to compile. But this is circumventing the
virtualenv and isn't safe behavior when installing into a
virtualenv.
I can easily set mxincludedir to a bogus directory
to trick it into thinking mx isn't installed anywhere and get it to
work, but that doesn't strike me as the best and cleanest
solution.
I'm not sure exactly what the best solution is overall, but I'd
suggest that one way or another, psycopg2 should only compile in
mx.DateTime support when it can both find the mx headers and know
that the mx python library will be available.
Daniele Varrazzo