Why is Python so hard to maintain

[RMJFlack]

can you provide minimal example with sample data so we can see what expected output(i.e. from python2)

I will try too. (Have to make a cut down version of the full prpgram).

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Aha, its coming together! It seems that in 2.7, a file that is opened as 'wb' will accept writing of strings. In 3.7, it expects bytes. So actually all my fussing about in the 3.7 version about converting struct.pack() back to strings (in order to do outfile.write(...) ) is actually unnecessary.
They didn't just change struct.pack(), they changed write() too. I'll post the cleaned up version in separate thread for critique, but I have two working test programs in 2.7 and 3.7.