Python: using sys.exit or SystemExit differences and suggestions

Question

Reading online some programmers use sys.exit, others use SystemExit.
Sorry for the basic question:

1. What is the difference?
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Answer 1

sys.exit(s) is just shorthand for raise SystemExit(s), as described in the former's docstring; try help(sys.exit). So, instead of either one of your example programs, you can do

sys.exit('Unable to open %s' % reference)