Firstable I am not a software expert just a hobby user so please be indulgent

I use a Raspberry Pi3B+ with raspbian lite and Python 3.5.3

In my script, I need 2 nested "while" loops so I chose two variables to incriment them 'i' and j. This script don't work and I made a certain time to understand (I did not think Python could play me a trick).

I needed to reset 'j' to go through the inner loop a few times and in fact I realized that when I initialized 'j', 'i' was also initialized !?!?

Very curious isn't it ?

I replaced 'i' by 'y' and no more problem, my script works very well.