Main.py

def binary_search(element, some_list, start_index = 0, end_index = None):
    if end_index == None:
        end_index = len(some_list) - 1

    if start_index > end_index:
        return None

    else:
        mid_index = int((start_index + end_index) / 2)

        if some_list[mid_index] == element:
            return mid_index

        elif element < some_list[mid_index]:
            return binary_search(element, some_list, start_index, mid_index - 1)

        else:

            return binary_search(element, some_list, mid_index + 1, end_index)

print(binary_search(2, [2, 3, 5, 7, 11]))
print(binary_search(0, [2, 3, 5, 7, 11]))
print(binary_search(5, [2, 3, 5, 7, 11]))
print(binary_search(3, [2, 3, 5, 7, 11]))
print(binary_search(11, [2, 3, 5, 7, 11]))

binary_search( ) 를 재귀함수로 만들 때 반드시 return을 해줘야 하는 것인가요?