Insertion Sort Big O

Insertion sort has a Big O of O(n^2), because that is its worst case complexity.

The outer loop of insertion sort always executes n times, while the inner loop depends on the input.

Best case: If the data is pre-sorted, insertion sort becomes really fast. Can you see why?
Average case: The average case is O(n^2) because the inner loop will execute about half of the time.
Worst case: If the data is in reverse order, it's still O(n^2) and the inner loop will execute every time.

Reference

def insertion_sort(nums):
    for i in range(len(nums)):
        j = i
        while j > 0 and nums[j - 1] > nums[j]:
            nums[j], nums[j - 1] = nums[j - 1], nums[j]
            j -= 1
    return nums