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A nested loop is a loop that is inside another loop. In other words, a loop is nested within another loop. Here's an example of a nested loop in Python:

Python

# initialize the outer loop variable i to 1
i = 1

# while the outer loop variable i is less than or equal to 3
while i <= 3:
    # initialize the inner loop variable j to 1
    j = 1

    # while the inner loop variable j is less than or equal to 3
    while j <= 3:
        # print the value of the outer and inner loop variables
        print(f"i = {i}, j = {j}")
        # increment the inner loop variable j by 1
        j = j + 1

    # increment the outer loop variable i by 1
    i = i +1

In this example, the outer while loop will execute 3 times, and the inner while loop will execute 3 times on each iteration of the outer loop. This means that the inner while loop will execute a total of 9 times.

Here's an example of iterating over a list of list

Python

# iterate over a list of lists

list_of_lists = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

for sublist in list_of_lists:

    # iterate over the elements in the current sublist

    for element in sublist:

        print(element)

Nested loops are useful for iterating over a list of lists, or for any situation where you need to loop over multiple sequences in a single block of code. By using nested loops, you can avoid writing separate loops for each sequence, which can make your code more concise and easier to read.

Nested Loops