teacher's merge sort

# teacher's merge sort
from random import randint

list_to_sort = [randint(1,100) for i in range(55)]
def merge1(list_a, list_b):
    list_c = []
    while len(list_a) > 0  and len(list_b) > 0:
        if list_a[0] < list_b[0]:
            list_c.append(list_a.pop(0))
        else:
            list_c.append(list_b.pop(0))
    if list_a == []:
        list_c += list_b
    else:
        list_c += list_a

    return list_c


def merge_sort1(unsorted):
    if len(unsorted) < 2:
        return unsorted
    else:
        middle = len(unsorted) // 2
        front = unsorted[:middle]
        back = unsorted[middle:]

        front = merge_sort1(front)
        back = merge_sort1(back)
    return merge1(front, back)

merge_sort1(list_to_sort)
print (list_to_sort)