Did you use language interop for matplotlib, or saving/loading data files?
I saved the data in .csv and then used that, because not only did I need/want to just plot the results, but I also wanted to explore and further analyse the data in a Jupyter Notebook.
Recently I've used Nim for the first time for an official project at my job (at university). Instead of doing a simulation with Python+Numpy, I've decided to do it with Nim, and just plot the results with matplotlib. The whole experience was very pleasant.
Speaking of interoperability with Python, there is a great Nim library called Nimpy [0], which makes possible to use Nim as a more pleasant Cython — you can keep writing Python, and just use Nim for the intensive/slow stuff.
[0] https://github.com/yglukhov/nimpy