First things first, you should really make that export into
PYTHONPATH=/home/jacos/qtreactor:$PYTHONPATH so as not to clobber anything that might be in there from system config files, &c, but prepend to it instead - additionally, you don't actually need to start it with "export" there. You'll want to run a new shell or run
source ~/.bashrc so that those changes take effect.
The default search path is always appended to $PYTHONPATH, according to my "man python", and you can get a look at it by opening a python shell and running the following:
That should give you an idea of what paths your python is searching in, and you may then be able to unpack into one of those directories.
As for the Right Way to do this, if qt4reactor should be available to anyone using the computer, stick it somewhere under /usr/lib/python (or better yet, /usr/lib/python[version], since python2.7 and python3 have noticeable differences...) and add that path to the PYTHONPATH of anyone using the machine by assigning it in /etc/bash.bashrc instead of ~/.bashrc. If it should be usable for only you, create a suitable folder in your home-directory and put the qt4reactor under that, so that if you need to add more python modules in the future you won't clutter up your home-folder too much. Obviously you'll need to change your additions to $PYTHONPATH in your ~/.bashrc as well. If you're the only user of this machine, then use whichever method you like - personally I'd go for the one that simulates multi-user machines, but that's because I run other boxen that do have multiple users and I think it's good to maintain good habits.