How to I get Emacs to use rst-mode inside of docstrings in Python files?  I vaguely remember that different modes within certain regions of a file is possible, but I don't remember how it's done.
As far as for edit-purposes, narrowing to docstring and activating rst-mode should be the way to go.
python-mode el provides py--docstring-p, which might be easily adapted for python.el
Than binding the whole thing to some idle-timer, would do the narrowing/switching.
Remains some expression which toggles-off rst-mode and widens.
Have Emacs edit Python docstrings using rst-mode