how does "for" loop works python?

Question

Why does it happen, that on four while-iteration "for loop" iterates only 2 times, while the array length is 3

import time
array = [[1, 1, 3], [2, 2, 3], [3, 3, 3]]

while True:
    #print (array)
    time.sleep(1)
    index = 0
    print (array)
    for proxy in array:
        
        print("iteration")
        if proxy[2] == 0:
            del array[index]
            continue
        
        proxy[2] -= 1
        index += 1
    print ("\n")

Compile

https://stackoverflow.com/questions/920645/when-to-use-while-or-for-in-python — Johnny John Boy, Jul 07 '22 at 14:58
This happens because you are deleting items from the array you are iterating over. Usually you don't want to do that — C_Z_, Jul 07 '22 at 15:02
Start debugging. This should make things clear for such a small example (Even pen & paper debugging should be sufficient for such a small example) — MrSmith42, Jul 07 '22 at 16:33

syter · Accepted Answer · 2022-07-07T15:03:21.577

1

When the last item of any of the arrays turns 0 (which happens after a few turns), you have the item deleted. This makes there only be 2 items instead of 3, and the for loop runs over those items, so it only iterates twice.

Edit::one good solution is to make a copy of the array, so that you can use one to delete items from, and one to iterate (loop) through

edited Jul 07 '22 at 15:03

answered Jul 07 '22 at 15:00

syter

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does "for" loop condition statement updates every iteration? – Timur Jul 07 '22 at 15:02
Yes, it updates realtime – syter Jul 07 '22 at 15:03

how does "for" loop works python?

1 Answers1