if

你在生活中是不是经常遇到各种选择，比如玩色子，猜大小，比如走那条路回家。python程序中也会遇到这种情况，这就用到了 if 语句

_username = 'zou'
_password = 'abc123'
username = input("username:")
password = input("password:")
if _username == username and _password == password:
    print("Welcome user {name} login...".format(name=username))
else:
    print("Invalid username or password!")
money = int(input("请输入你兜里的钱:"))
if money > 500:
    print("吃啤酒吃炸鸡. 生活美滋滋")
elif money > 300:
    print("盖浇饭走起")
elif money > 50:
    print("方便面走起")
else:
    print("减肥走起")

while

在生活中，我们遇到过循环的事情吧？比如循环听歌，在程序中，循环也是存在的，

count=0
while True:
    print("count:",count)
    count=count+1

陷入了死循环，在实际项目中要避免出现死循环，True 的T必须是大写

age_of_oldboy = 56
while True:
    guess_age = int(input('guess age:'))
    if guess_age == age_of_oldboy:
        print("yes, you got it. ")
    elif guess_age > age_of_oldboy:
        print("think smaller...")
    else:
        print("thing bigger...")

一直可以输入，对或错都不结束

age_of_oldboy = 56
while True:
    guess_age = int(input('guess age:'))
    if guess_age == age_of_oldboy:
        print("yes, you got it. ")
        break
    elif guess_age > age_of_oldboy:
        print("think smaller...")
    else:
        print("thing bigger...")

加了个break，输入正确时退出
break 结束循环. 停止当前本层循环

age_of_oldboy = 56
count = 0
while count < 3:
    guess_age = int(input('guess age:'))
    if guess_age == age_of_oldboy:
        print("yes, you got it. ")
        break
    elif guess_age > age_of_oldboy:
        print("think smaller...")
    else:
        print("thing bigger...")
    count = count + 1

输错三次退出循环

age_of_oldboy = 56
count = 0
while count < 3:
    guess_age = int(input('guess age:'))
    if guess_age == age_of_oldboy:
        print("yes, you got it. ")
        break
    elif guess_age > age_of_oldboy:
        print("think smaller...")
    else:
        print("thing bigger...")
    count = count + 1
else:
    print("you have tried too many times...")

当程序正常执行完会执行最后一个else，如果中间遇到break，不执行else

while True:
    s = input("请开始说:")
    if s == 'q':
        break  # 停止当前循环
    # 过滤掉马化腾
    if "马化腾" in s:  # 在xxx中出现了xx
        print("你输入的内容非法. 不能输出")
        continue  # 停止当前本次循环.继续执行下一次循环
    print("喷的内容是:"
count = 1
while count <= 10:
    print(count)
    count = count + 1
    if count == 5:
        break  # 彻底停止循环. 不会执行后面的else
else:  # while条件不成立的时候执行
    print("这里是else")

 continue：停止本次循环，继续执行下一次循环