insertion sort time complexity

import time, random

def insertion_sort(lst):
    length = range(1, len(lst))
    for i in length:
        value = lst[i]

        while lst[i-1] > value and i > 0:
            lst[i], lst[i - 1] = lst[i - 1], lst[i]
            i = i - 1

    return(lst)

def random_element_listt():
    global listt

    #NUMBERS FROM 0-999
    #PICKS RANDOM NUMBER AND PUTS IT IN LISTT
    for i in range(1000):
        listt.append(random.choice(range(1, 1000)))

listt = []

def main():
    random_element_listt()

    print()
    print("INSERTION SORT")
    print()
    t1 = time.time()
    print(insertion_sort(listt))
    t2 = time.time()
    print('elapsed time=', t2 - t1)
    print('Big O Notation: O(n^2)')

main()
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