Finishing a matplotlib project- Plotting a graph.

Python Creating a solar system using python, matplotlib. The results of the simulation are returned on a matplotlib graph. I have a graph of all of the orbits, that works fine. I just need to implement a 'Change in system kinetic energy over time' plot, which I keep failing to actually return a result on, I either get an error or blank graph, I have 4 files: A particle file: Contains a particle class that has a way of defining different variables for a massive particle. Used this to define all the planets. A Solar System file: Contains a class that has functions in to update things like position and gravitational acceleration. It has a kinetic energy function in it and that's what I'm trying to plot A test file: Takes all the data over a given interval with a time step attached and updates it, saves the data as a [login to view URL] file. An Analysis file: Loads the [login to view URL] file and then is used to plot the data. my project plots all the orbits fine, I just can't seem to get the kinetic energy to plot and that's where I'm falling down. The project is pretty much finished, it's just getting a plot of the kinetic energy of the system over the period as I already have all the velocities, masses and times etc, even have a kinetic energy function, it's just implementing it in the analysis part to return a plot. Thanks!