# 函数的嵌套调用：在一个函数内部调用另一个函数 def fn1():     pass def fn2():     fn1()  # 函数的嵌套调用 def fn3():     fn2()  # 函数的嵌套调用 fn3() # 案例： # 求两个数最大值 def max_two(n1, n2):     if n1 > n2:         return n1     return n2 # 求三个数最大值 def max_three(n1, n2, n3):     max = max_two(n1, n2)     return max_two(max, n3) # 求四个数最大值 def max_four(n1, n2, n3, n4):     max = max_three(n1, n2, n3)     return max_two(max, n4) print(max_four(20, 50, 30, 50))