Jenks natural breaks for CPT files?

I have a script iterating through a few million rows of data to generate a few hundred maps of various year/species combinations.

It generates a cpt file for each map based on the data, with two options, equidistant over the data range, or equal counts per colour (not using makecpt - inline code in the script does the calculations). 


I'd like to add a third option, which I'm not sure how to implement. Cartographically, a more informative colour table can be provided using natural breaks instead of the two approaches described above, but I'm not sure how to do this. Ideally I feed a set of z values into a bit of code, along with the number of classes & get the set of break values. 

Does anyone know of a way to generate the break values from a set of Z values?

Thanks,

   Brent Wood

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