using xrange output not expected

Question

s = 0

for s in xrange(0, 100):
    print "s before", s
    if s % 10 == 0:
        s += 10
    print "s after", s

result of loop1

s = 0

while s < 100:
    print "s before", s
    if s % 10 == 0:
        s += 10
    s += 1
    print "s after", s

result of loop2

As pictures shown above, why those 2 loops doing similar things, one using xrange while another using while-loop are giving me exact different output?

Because for sets s from the iterable, and setting s to something else in the loop doesn't change the iterable. — Martijn Pieters
– Martijn Pieters, Commented Aug 9, 2017 at 8:35
You are essentially asking why s = first_thing then s = second_thing didn't change first_thing. — Martijn Pieters
– Martijn Pieters, Commented Aug 9, 2017 at 8:36

Mohamed Ali JAMAOUI · Accepted Answer · 2022-04-17 08:29:33Z

2

s in the first loop is overwritten by the values coming from xrange(0, 100) whereas in the second loop you are manually initializing the variable s=0 and then incrementing it with s += 10. So, it's exactly the expected behavior.

You need to have a look into variable scopes in python. Check this discussion: Short description of the scoping rules?

edited Apr 17, 2022 at 8:29

answered Aug 9, 2017 at 8:36

Mohamed Ali JAMAOUI

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2 Comments

Sam Y Over a year ago

Thank you very much for ur answer and ur link shared.

Sam Y Over a year ago

Thanks very much and sorry for the late reply. And most importantly, you solved my problem.

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