Suppose you want to generate a pdf file with matplotlib and save it.

genfigure.py:

import matplotlib.pyplot as pltimport sysplt.plot([0, 1], [0, 1])plt.savefig(sys.argv[1])

Run the script from the command line

$ python genfigure.py 1.pdf$ python genfigure.py 2.pdf

Given that we are saving the same figure, we would expect the output to be the same. However, after looking at the file hashes, they appear to be different. In my particular case:

$ md5sum 1.pdf 2.pdfe54cdbd65a6baaa5152d90743d800039  1.pdf4b0ac2a7c046c4813114c63f3c4d27e7  2.pdf

On the other hand, no such issue exists when saving png files.

$ python genfigure.py 1.png$ python genfigure.py 2.png

The twopng files are exactly the same

$ md5sum 1.png 2.png5d22187827337cd9262ee248550fab6f  1.png5d22187827337cd9262ee248550fab6f  2.png

It appears that pdf saving has some source of non-determinism.

Is there a way to ensure that saving the same figure multiple times, results in exactly the same pdf file?