This is simply an effect of you having full knowledge of Ruby development management, but not python's. In fact, they are quite similar to eachother.

A pythonist would just say:

"I just install a python environment from virtualenv, git clone an app and type 'pip install -r requirements.txt' and then its all working."

virtualenv ~= rbenv, and pip ~= bundler.

Either set of the two make it easy to install appropriate packages for separate projects.

Now maybe the googleability of this knowledge isn't as great as it could be, but ask any good pythonista and they'll set you on the right track.