Python实现分数序列求和

#!/usr/bin/env python

# coding:UTF-8

  

  

"""

@version: python3.x

@author:曹新健

@contact: [e-mail]

@software: PyCharm

@file: 1223.py

@time: 2018/12/23 20:56

"""

  

'''

有一分数序列：2/1，3/2，5/3，8/5，13/8，21/13...求出这个数列的前20项之和。

'''

"""

#方法一

def g(n):

   if n <= 2:

     return n

   else:

     return g(n-1) + g(n-2)

sum = 0

for i in range(1,21):

   sum += g(i+1)/g(i)

print(sum)

"""

  

#方法二

numerator = 2

denominator = 1

sum = 0

while True :

   try :

     n = int ( input ( "请输入一个整数：" ))

   except ValueError:

     print ( "输入错误，请输入整数" )

   else :

     for i in range (n):

       sum + = numerator / denominator

       numerator, denominator = numerator + denominator, numerator

  

     print ( sum )

     break