We usually stick to the official Debian python-* packages (if they exist upstream). When they don't we use python-virtualenv[1][2] to pull specific versions and dependencies from pip into a virtual env.

Now when we build our Debian package (debian/rules):

  override_dh_virtualenv:
    	dh_virtualenv -p myproj --use-system-packages

[1] https://github.com/spotify/dh-virtualenv [2] https://packages.debian.org/jessie/python/python-virtualenv