Matplotlib is a python 2D plotting library which produces publication quality figures in a variety of hardcopy formats and interactive environments across platforms. Matplotlib can be used in python scripts, the python and ipython shell (ala MATLAB®* or Mathematica®†), web application servers, and six graphical user interface toolkits.
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Venn Diagrams / Set Intersections
For visualizing the overlap of two or three sets, matplotlib-venn is a useful package that can take as input Python sets to create proportional Venn diagrams.