csv - Accessing existing instance of QGIS from stand-alone python script

For my own data analysis pipeline, I am running a split screen setup with iPython notebooks on one side, generating variables from source data, pushing them to a CSV file which QGIS then reads/joins to an appropriate geography, instantly visible on the other side of the screen.

I would like to push the control of the running instance of QGIS to the ipython notebook, in effect allowing a super quick calculation/visualization cycle. Right now I can do this in the QGIS python console with something like this:

canvas = qgis.utils.iface.mapCanvas()
cLayer = canvas.currentLayer()
canvas.refresh() 

but I would like to:

1. connect to an existing instance of qgis from an external python environment


2. at a minimum refresh the map, after each re-write to the csv from ipython notebook, but preferably


3. re-calculate breaks (using quantiles, natural breaks) based on the newly joined values

Any pointers appreciated!