Matplotlib: what is it?
The matplotlib library enables you a fast and accessible way of plotting publication quality figures, which can be output in a variety of formats. Matplotlib’s pyplot offers a MATLAB style interface for creating and customising your plots. A few images of what is possible include:
For more information, look at the matplotlib home page and take a look at the gallery.
This library can be used with all sorts of python formats and is useful for visualising arrays of data such as created using numpy - if you are unfamiliar with numpy, take a look here.