[reproducibility] Update code to Python 3

[cthoyt]

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Python 2's end of life support happened last year, so it would be good to make this code run on modern versions of Python.

I'd be happy to submit a PR for this. There's a tool called 2to3 built in in python that can take care of this (https://docs.python.org/3/library/2to3.html)

It can be done with the following code (when there's a valid python3 installation available):

$ 2to3 -w predict.py
$ 2to3 -w predict_enriched.py