I have 3 machines (raspberry pi's). One has a database of sensor readings on, the other two are 'slave' devices that read/run various sensors. what is the best solution to allow the 'master' pi to access sensor readings on the 'slave' pis- so it can save the values to the database.
All the pis are on the same internal network, and will never be on the internet
The 'slave' pis return integers to the master pi, that is all.
It has to be python3 (because the software that queries the sensors is)
What is the very simplest way?

Some kind of web service? I've so far failed to get get pysimplesoap and cherrypy to work on python3. 
Something else? Pyro? It seems a bit complicated just to get back 2 integers. 
Roll my own with sockets (that can't be the easiest way?!)
Give up and put a mysql database on each pi, then make the 'sensor-value-reporting-website' stretch across 3 databases/hosts.
I would have a mySQL database on the master only and have the slaves write their own tables to that database using the cymysql python3 module
(pip3 install cymysql)
Python machine-communication on raspberry pi