python--if，while，break，continue

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