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

s = 0

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

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?

Answer 1

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?