While loop inside While loop in python?

Question

I am a beginner in python.

The second loop only run for once, the first time only, but when the turn comes to the first loop and when e = e+1 - python skips the second loop!

Why?

The print order only work for once.

 items  = [['.', '.', '.', '.', '.', '.'],
    ['.', 'O', 'O', '.', '.', '.'],
    ['O', 'O', 'O', 'O', '.', '.'],
    ['O', 'O', 'O', 'O', 'O', '.'],
    ['.', 'O', 'O', 'O', 'O', 'O'],
    ['O', 'O', 'O', 'O', 'O', '.'],
    ['O', 'O', 'O', 'O', '.', '.'],
    ['.', 'O', 'O', '.', '.', '.'],
    ['.', '.', '.', '.', '.', '.']]
i=0
e=0
while e < 6 :
    while i < 9 :  #python run this loop only once, and never come back when e=e+1
          print items[i][e]
          i=i+1
    e=e+1

Debugged this myself, changed the print to just print foo and added a print to the outer while to print bar, foo prints 9 times, bar prints 6 times after that's done. Is this not the expected behaviour — L_Church
– L_Church, Commented May 1, 2018 at 14:05
i will try it , coz i haven't use 'print foo' before, i am using python 2.7 , thanks for this information :) — Iris
– Iris, Commented May 2, 2018 at 15:14
it doesn't do anything special i just used it so i could see how the loops worked — L_Church
– L_Church, Commented May 2, 2018 at 15:17

leo · Accepted Answer · 2018-05-01 14:05:11Z

After the 'i' loop runs once, i will be set to 9 and will stay as 9 until you reset. so you can try to set it to 0 after e = e+1. A useful technique you can try is also printing the values of 'e' and 'i' to see where the loops gone wrong

items  = [['.', '.', '.', '.', '.', '.'],
    ['.', 'O', 'O', '.', '.', '.'],
    ['O', 'O', 'O', 'O', '.', '.'],
    ['O', 'O', 'O', 'O', 'O', '.'],
    ['.', 'O', 'O', 'O', 'O', 'O'],
    ['O', 'O', 'O', 'O', 'O', '.'],
    ['O', 'O', 'O', 'O', '.', '.'],
    ['.', 'O', 'O', '.', '.', '.'],
    ['.', '.', '.', '.', '.', '.']]
i=0
e=0
while e <6 :
    while i <9 : 
          print items[i][e]
          print 'loop: i'+str(i)+'e'+str(e)
          i=i+1
    e=e+1
    i=0

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