程序媛进阶之路——函数调用

给不同的人物打印歌曲

def happy():
    print("happy,happy birthday to you")
def sing(person):
    happy()
    print("happy,happy",person+"!")
    happy()

判断三角形并计算其周长

import math
def square(x):
    return x*x
def distance(x1,y1,x2,y2):
    dist=math.sqrt(square(x1-x2)+square(y1-y2))
    return dist
def isTriangle(x1,y1,x2,y2,x3,y3):
    flag=((x1-x2)*(y3-y2)-(x3-x2)*(y1-y2))!=0
    return flag
def main():
    print("please enter (x,y) pf theses in return:")
    x1, y1 = eval(input("point1:(x,y)="))
    x2, y2 = eval(input("point2:(x,y)="))
    x3, y3 = eval(input("point3:(x,y)="))
    if(isTriangle(x1,y1,x2,y2,x3,y3)):
        perim=distance(x1,y1,x2,y2)+distance(x2,y2,x3,y3)+distance(x1,y1,x3,y3)
        print("the triangle is{0:0.2f}".format(perim))
    else:
        print("kidding me?it is")

银行账户计算利率

def addinterest(balance,interest):
    newbalance=balance*(1+interest)
    balance=newbalance
def main():
    amount=1000
    rate=0.002
    addinterest(amount,rate)
    print(amount)

运行后我们发现输出amount只有1000
这与python实参和形参的调用机制有关
函数的形参只接受了函数实参的值，给形参赋值并不影响实参
因此需要将代码进行改进

def addinterest(balance,interest):
    newbalance=balance*(1+interest)
    return newbalance
def main():
    amount=1000
    rate=0.002
    amount=addinterest(amount,rate)
    print(amount)

程序的递归

有一个或多个递归列是不需要递归的
所有的递归列都要以一个基规列结尾
条件：
1、调用函数自身
2、设置正确的函数

def main(n):
    if n == 1:
        return 1
    else:
        return n = main(n-1)
number=int(input('put a number please'))
result=main(number)
print("%dthe number is:%d" % (number,result))

字符串的反转
构造递归函数需要基例
基例不进行递归，否则递归就会无限循环进行

def reverse(s):
 if s==""：
  return s
 else:
 return reverse(s[1：])+s[0]