python's fifteenth day for me 递归函数

递归...

def age(n):
    if n == 1:
        return 18
    else:
        return age(n-1)+2   # 反复调用函数age()
print(age(4))

l = [1,3,5,7,9,11]
def two_search(li,aim,start = 0,end = None):
    end = len(li)-1 if end is None else end
    mid_index = (end - start) // 2 + start
    if start <= end:
        if li[mid_index] > aim:
            return two_search(li,aim,start = 0 ,end = mid_index-1)
        elif li[mid_index] < aim:
            return two_search(li,aim,start = mid_index+1,end = end)
        elif li[mid_index] == aim:
            return mid_index
        else:return '无此值'
    else:return '无此值'
print(two_search(l,7))          # 3