matplotlib
Matplotlib is a library with a very 'Matlab' like environment for generating publication quality figures. You can output to raster formats (e.g., PNG, TIFF, JPG) immediately in a pop-up window or to vector (e.g, EPS, PS) formats that are saved as files. The style of graphs and syntax for creating them, especially when combined with the added Python language constructs through NumPy will be very familiar to users of Matlab.
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