pylint: Using possibly undefined loop variable 'n'

Question

Pylint say

W:  6: Using possibly undefined loop variable 'n'

with this code:

iterator = (i*i for i in range(100) if i % 3 == 0)

for n, i in enumerate(iterator):
    do_something(i)

print n

because if the iterator is empty (for example []) n is undefined, ok. But I like this trick. How to use it in a safe way?

I think that using len(list(iterator)) is not the best choice because you have to do two loops. Using a counter, and incrementing it I think it's not very pythonic.

Answer 1

Have you considered merely initializing n to None before running the loop?

Answer 2

Define a default value for n before the for statement:

iterator = (i*i for i in range(100) if i % 3 == 0)

n=None
for n, i in enumerate(iterator):
    do_something(i)

print n