Python nested for loop using same variable [duplicate]

Question

Out of curiosity, I tried implementing a nested for loop using the same iterating variable in both the outer and inner for loops.

for i in range(3):
    for i in range(4):
        print("i = %s" % i)

What exactly is going on behind the scene here? BTW, the inner print is executed 12 times.

The for statement does not use i for looping. It just assigns current iteration value to i before running loop body. That's why it runs fine. The print will only show inner for's i values though. — spectras
– spectras, Commented Aug 17, 2017 at 10:58
The inner loop rewrites the outer i variable. This is fine as long as you aren't doing anything with it. — cs95
– cs95, Commented Aug 17, 2017 at 10:59
@omu_negru Um, that's not a Python question, so that logic doesn't quite apply here. ;) — PM 2Ring
– PM 2Ring, Commented Aug 17, 2017 at 11:03

Aviad · Accepted Answer · 2017-08-17 11:00:32Z

1

The variable "i" is iterating the elements in the outer loop, but then is re-set to iterate the elements in the inner loop. And so on. The bottom line is that you're gonna print the elements of the inner loop 3 times (the size of the outer one)

answered Aug 17, 2017 at 11:00

Aviad

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omu_negru · Accepted Answer · 2017-08-17 11:00:43Z

1

What happens is that the second i shadows the first one, so the print instruction will only reffer to the inner loop i

answered Aug 17, 2017 at 11:00

omu_negru

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