Single step through Notebook cell or external file invoked by Notebook cell

I am looking at using PyCharm to develop IPython Notebooks.

Recently I've been loading up the notebook in my web browser and using an external text editor for auxiliary .py files.  This creates for incredibly clumsy debugging. Basically inserting print statements or breaking out into pdb. http://stackoverflow.com/questions/39465752/how-to-debug-external-py-functions-run-from-jupyter-ipython-notebook 

It would be lovely to be able to single step through each line in a notebook cell.  Does PyCharm allow this?

Also, how about signal stepping through each line in a .py that is invoked from within a notebook cell.  Is it possible to do this?

Could someone possibly have a go and see if they can get it working, and post back instructions if successful?

π