Looping 300 000 rows in Python

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How to loop over 300 000 rows and edit each row string one by one?

I have a list of 11-digit numbers stored in one single column in Excel, and I need to separate the digits according to this pattern: 2-2-1-3-3.

I use the code below to loop to test the solution for only 20 rows and it's working.

Example: 00002451018 becomes 00 00 2 451 018.

priceListTest contains the column Column1 which has these 11 digit numbers. Somehow I need to loop all over these 300 000 rows and use the get_slices to change the pattern for each row like from the example above and store it into the new column New Value.

The for index, row it's working very slowly when I have to use it for 300 000 rows. Maybe there is a better method, but I'm new to python.

Thanks in advance!

What I have tried:

for index, row in priceListTest.iterrows(): 
    #print(index,row)
    def get_slices(n, sizes, n_digits=11):
        for size in sizes:
            n_digits -= size
            
            val, n = divmod(n, 10 ** n_digits)
            yield f'{val:0{size}}'

    n = row['Column1']
    newVar = (' '.join(get_slices(n, [2, 2, 1, 3, 3])))
    priceListTest.at[index,['New Value']] = newVar