How to reset the index number of for loop in python

Question

for x in range(len(pallets_data_list)):
    """
    SOME CODE
    """
    if pallets_data_list[x]['data_id'] == 32:
        # Go back and search again in for loop

In above code, I have a for loop which is iterating over pallets_data_list. Inside this for loop, if the condition becomes True, I need to go back to for loop and start iterating again from 0. Lets consider that the condition becomes True at x = 20.

To reset x, I am setting it to 0 and then using continue like below:

    if pallets_data_list[x]['data_id'] == 32:
        # Go back and search again in for loop
        x = 0
        continue

Using continue, its going back to for loop but x is not reset and starts iterating from 21. Is there any way, I can reset x again back to 0. Can anyone please suggest any good solution. Please help. Thanks

Does this answer your question? python: restarting a loop

b-fg
– b-fg

2020-04-10 08:42:38 +00:00
Commented Apr 10, 2020 at 8:42 — b-fg
– b-fg, Commented Apr 10, 2020 at 8:42

Nick · Accepted Answer · 2020-04-10 08:32:38Z

3

You need to be careful not to create an infinite loop by resetting the index. You can use a while loop with a found flag to avoid that:

pallets_data_list = [1, 4, 6, 32, 23, 14]

x = 0
found = False
while x < len(pallets_data_list):
    print(pallets_data_list[x])
    if not found and pallets_data_list[x] == 32:
        found = True
        x = 0
        continue
    x += 1

Output:

answered Apr 10, 2020 at 8:32

Nick

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Comments

norok2 · Accepted Answer · 2020-04-10 08:39:59Z

3

Simply do not use a for loop but a while loop.

The following for loop (which does not work):

for i in range(n):
    ...
    if condition:
        i = 0

should be replaced by:

i = 0
while i < n:
    ...
    if condition:
        i = 0
    else:  # normal looping
        i += 1

or, with continue:

i = 0
while i < n:
    ...
    if condition:
        i = 0
        continue
    i += 1

When using while beware of possible infinite looping. Possible strategies to avoid infinite looping include using a flag or including an extra counter that limits the maximum number of iterations regardless of the logic implemented in the body.

edited Apr 10, 2020 at 8:39

answered Apr 10, 2020 at 8:30

norok2

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2 Comments

S Andrew Over a year ago

and what is n here in while loop

norok2 Over a year ago

@SAndrew Sorry I thought it was clear from the "equivalent except not working for loop". n is the argument of range() in the for loop code, i.e. the number of times the loop would execute should the condition never be True.

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