【20171002】python_语言设计（3）函数

1.函数定义
完成特定功能的一个语句组，函数可以反馈结果
为函数提供不同的参数，可以实现对不同数据的处理。
自定义函数、系统自带函数（python内嵌函数，标准库函数、图形库）
使用函数的目的：降低编程的难度、代码重用
函数定义：def语句。def (<参数>)：

形式参数、实际参数
函数调用：(<参数>)
return语句：结束函数调用，并将结果返回给调用者。

#打印生日快乐def happy():    print("happy birthday to you !")def main(str1):    happy()    happy()    print("happy birthday to"+"dear "+str1)    happy()     main("mike")

2.函数调用和返回值
无返回值：return None
返回值可以是变量和表达式，可以返回一个或多个。

#两点间距离import mathdef distance(x1,x2,y1,y2):    a=(x1-x2)*(x1-x2)    b=(y1-y2)*(y1-y2)    dist=math.sqrt(a+b)    return dist def main():    x1,y1,x2,y2=eval(input())    distance(x1,x2,y1,y2)    print("distance=",distance(x1,x2,y1,y2))main()

#三角形周长import mathdef square(x):    return x*x  def distance(x1,y1,x2,y2)    dist=math.sqrt(square(x1-x2)+square(y1-y2))    return distdef isTriangle(x1,y1,x2,y2,x3,y3):    flag=((x1-x2)*(y3-y2)-(x3-x2)*(y1-y2))!=0    return flagdef main():    print("输入三个点的坐标：")    x1,y1=eval(input())    x2,y2=eval(input())    x3,y3=eval(input())    if(isTriangle(x1,y1,x2,y2,x3,y3)):        perim=distance(x1,y1,x2,y2)+distance(x2,y2,x3,y3)+distance(x1,y1,x3,y3)    else :        print("wrong!")main()

3.改变参数的函数值

#银行利率计算def addInterest(balance,rate):    newBalance=balance*(1+rate)    return newBalance    #balance=newBalancedef main():    amount=1000    rate=0.05    amount=addInterest(amount,rate)    print(amount)main()

#多个银行账户的程序利率计算def addInterest(balance,rate):    for i in range(len(balances))        balance[i]=balance[i]*(1+rate)def main():    amounts=[1000,105,3500,739]    rate=0.05    addInterest(amounts,rate)    print(amounts)main()

4.函数程序结构与递归

def createTable(principle,apr):    #为每一年绘制星号的增长图    for year in range(1,11):        principle=principle*(1+apr)        print("%2d"%year,end='')        total=caculateNum(principle)        print("*"*total)    print(" 0.0K   2.5K   5.0K  7.5K  10.0K")def caculateNum(principle):    #计算星号数量    total=int(principle*4/1000.0)    return totaldef main():    print("This program plots the growth of a 10-year investment")    #输入本金和利率    principle=eval(input("enter the initial principal: "))    apr=eval(input("enter the rate:"))    #建立图表    createTable(principle,apr)main()

递归计算

#递归def fact(n):    if n==0:        return 1    else :        return n*fact(n-1)def main():    print(fact(3))main()

#字符串反转def reverse(s):    if s=="":        return s    else :        return reverse(s[1:])+s[0]def main():    print(reverse("ajdifjoi"))main()

5.函数实例分析

# drawtree.pyfrom turtle import Turtle, mainloopdef tree(plist, l, a, f):    """ plist is list of pens    l is length of branch    a is half of the angle between 2 branches    f is factor by which branch is shortened    from level to level."""    if l > 5: #        lst = []        for p in plist:            p.forward(l)#沿着当前的方向画画Move the turtle forward by the specified distance, in the direction the turtle is headed.            q = p.clone()#Create and return a clone of the turtle with same position, heading and turtle properties.            p.left(a) #Turn turtle left by angle units            q.right(a)# turn turtle right by angle units, nits are by default degrees, but can be set via the degrees() and radians() functions.            lst.append(p)#将元素增加到列表的最后            lst.append(q)        tree(lst, l*f, a, f)def main():    p = Turtle()    p.color("green")    p.pensize(5)    #p.setundobuffer(None)    p.hideturtle() #Make the turtle invisible. It’s a good idea to do this while you’re in the middle of doing some complex drawing,    #because hiding the turtle speeds up the drawing observably.    #p.speed(10)   # p.getscreen().tracer(1,0)#Return the TurtleScreen object the turtle is drawing on.    p.speed(10)    #TurtleScreen methods can then be called for that object.    p.left(90)# Turn turtle left by angle units. direction 调整画笔    p.penup() #Pull the pen up – no drawing when moving.    p.goto(0,-200)#Move turtle to an absolute position. If the pen is down, draw line. Do not change the turtle’s orientation.    p.pendown()# Pull the pen down – drawing when moving. 这三条语句是一个组合相当于先把笔收起来再移动到指定位置，再把笔放下开始画    #否则turtle一移动就会自动的把线画出来    #t = tree([p], 200, 65, 0.6375)    t = tree([p], 200, 65, 0.6375)main()