Fix preprocessed python3 scripts

[jeking3]

#68 was incomplete; I finished this for modern python3 and checked that the script can run. The only incompatible issue was that files were opened with "rU" and the "U" is no longer valid. I updated the README, but I did not regenerate the files. When I did, it wouldn't build in CI.

This fixes #67

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.73%. Comparing base (4b81600) to head (04d2348).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop      #87   +/-   ##
========================================
  Coverage    94.73%   94.73%           
========================================
  Files            5        5           
  Lines           19       19           
  Branches         3        3           
========================================
  Hits            18       18           
  Misses           1        1           

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