S_str must be a positive integer greater than 0.

[smutt]

Line 54:
S_str must be a positive integer greater than 0.

Currently we only check that it can be cast to an INT.

https://docs.python.org/3/library/functions.html#int

[paulehoffman]

Good catch. Fixed by e910e90

[smutt]

That's a rather overcomplicated hack. The indentation isn't even correct.

How about?

try:
S = int(S_str)
if S < 1:
raise ValueError('S must be a whole number')
except as err:
print(repr(err))
sys.exit(1)