python 分支结构 循环结构

1.在Python中，要构造分支结构可以使用`if`、`elif`和`else`关键字。所谓关键字就是有特殊含义的单词，像`if`和`else`就是专门用于构造分支结构的关键字。

2.在Python中构造循环结构有两种做法，一种是`for-in`循环，一种是`while`循环。

3.代码实例如下

#输入用户名和密码，正确登陆，否则错误username = input(‘Users:‘)password = input(‘Password:‘)

if username == ‘admin‘ and password == ‘123‘:    print(‘login‘)else:    print(‘Error.‘)

#注册的密码必须有大写小写和数字password = input(‘>>‘)A = ‘ASDFLKKJIHBBUIVFBLJOEYT‘B = ‘assdlgt9bjknkfldnpen‘C = ‘1234567890‘count1,count2,count3 = False,False,Falsefor i in password:    if i in A :        count1 = True    if i in B:        count2 = True    if i in C:        count3 = Trueif count1 and count2 and count3:    print(‘OK‘)else:    print(‘必须含有大写小写和数字‘)

#分段函数x = float(input(‘x=‘))if(x>1):   y=3*x-5elif(x>=-1):   y=x+2else:    y=5*x+3print(x,y)

#计算器num1,num2 = map(float,input(‘Num1,Num2‘).split(‘,‘))choose_method = input(‘Choose Method:[+,-,*,/]‘)if choose_method in ‘+-*/‘:    if choose_method =="+":        print(‘%.2f + %.2f = %.2f‘%(num1,num2,num1+num2))    elif choose_method ==‘-‘:        print(‘%.2f - %.2f = %.2f‘%(num1,num2,num1-num2))    elif choose_method ==‘*‘:        print(‘%.2f * %.2f = %.2f‘%(num1,num2,num1*num2))    else :        print(‘%.2f / %.2f = %.2f‘%(num1,num2,num1/num2))

else:    raise KeyError(‘Only choose [+,-,*,/]‘)

#输入三条边长如果能构成三角形就计算周长和面积x = float(input(‘请输入x‘))y = float(input(‘请输入y‘))z = float(input(‘请输入z‘))import mathif x+y>z and x+z>y and z+y>x:     print(‘周长是：%f‘ %(x+y+z))     p=(x+y+z)/2     area=math.sqrt(p*(p-x)*(p-y)*(p-z))     print(‘面积： %f‘%(area))

else:     print(‘不能构成三角形‘)

#银行卡密码 用户只能输入三次密码，如果密码错误，则锁定账号ini_passward = 100000input_ = int(input(‘请输入密码>>:‘))for i in range(2):    if input_ == ini_passward:        print(‘OK‘)        break    else:        print(‘密码错误,请尝试重新输入‘)        input_ = int(input(‘请输入密码:>>‘))else:    print(‘账号锁定‘)

#猜数字游戏计算机出一个1~100之间的随机数由人来猜计算机根据人猜的数字分别给出提示大一点/小一点/猜对import randomanswer = random.randint(1, 100)counter = 0while True:    counter += 1    number = int(input(‘请输入: ‘))    if number < answer:        print(‘大一点‘)    elif number > answer:        print(‘小一点‘)    else:        print(‘恭喜你猜对了!‘)        breakprint(‘你总共猜了%d次‘ % counter)if counter > 7:    print(‘你的智商余额明显不足‘)```

原文地址：https://www.cnblogs.com/jklp-1234/p/11287713.html