Python 递归函数

１、最简单的递归函数：求阶乘

def fact(n):
    if n==1:
        return 1
    return n*(fact(n-1))

问题：fact(1000)将出现栈溢出

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "D:\pythons\fact.py", line 4, in fact
    return n*(fact(n-1))
  File "D:\pythons\fact.py", line 4, in fact
    return n*(fact(n-1))
  File "D:\pythons\fact.py", line 4, in fact
    return n*(fact(n-1))
  [Previous line repeated 994 more times]
  File "D:\pythons\fact.py", line 2, in fact
    if n==1:
RecursionError: maximum recursion depth exceeded in comparison

优化：尾递归

def fact(n):
    return fact_iter(n,1)

def fact_iter(num,product):
    if num==1:
        return product
    return fact_iter(num-1,num*product)