Bubble Sort seems difficult

Hey Shardul,

Thank you for your question!

Let's take as an example the list used in the lecture, namely:

data = [53,76,25,98,56,42,69,81]

Its length is 8. Therefore, the iterator i ranges from 0 to 8-1 = 7.

Now, note the following relationship between the iterators i and j:
*For i = 0, j ranges from 0 to 8-0-1 = 7 exclusive (therefore, from 0 to 6)
*For i = 1, j ranges from 0 to 8-1-1 = 6 exclusive (therefore, from 0 to 5)
*For i = 2, j ranges from 0 to 8-2-1 = 5 exclusive (therefore, from 0 to 4)
*For i = 3, j ranges from 0 to 8-3-1 = 4 exclusive (therefore, from 0 to 3)
*For i = 4, j ranges from 0 to 8-4-1 = 3 exclusive (therefore, from 0 to 2)
*For i = 5, j ranges from 0 to 8-5-1 = 2 exclusive (therefore, from 0 to 1)
*For i = 6, j ranges from 0 to 8-6-1 = 1 exclusive (therefore, from 0 to 0)
*For i = 7, j ranges from 0 to 8-7-1 = 0 exclusive (we don't enter the second for-loop).

The purpose of the first for-loop is to loop through the whole list. The purpose of the second for-loop is to loop through the unsorted part of the list. Below, I have modified Giles' code by adding a couple of print-statements to guide you through the algorithm:

data_copy = data[:]

for i in range(len(data_copy)):

    for j in range(0, len(data_copy)-i-1):
        print(f'i: {i}')
        print(f'j: {j}')

        print(f'{data_copy[j]}, {data_copy[j+1]}')
        if data_copy[j] > data_copy[j+1]:
            data_copy[j], data_copy[j+1] = data_copy[j+1], data_copy[j]
            print(f'Entered the if-statement and swapped the numbers: {data_copy}\n')
        else:
            print(f'So far, the list is sorted: {data_copy}\n')

print(f'\n{data_copy}')

Note that the list is being sorted from the back to the front, that is, pushing the biggest numbers towards the end of the list, leaving the front unsorted.

Hope this helps! Let me know if something remains unclear.

Kind regards,
365 Hristina