while 的用法

while作用：只要…条件成立，就一直做…。永远为True的循环，俗称死循环。但在循环过程中，制造某种可以使循环停下来的条件，就可以停止它。要免编写无限循环，务必对每个while环进行测试，确保它像预期那样结束。

1.使用while计数，while的意思就是当条件成立时，执行while内的判断。

count = 0
while True:    #while的意思就是这个条件成立的时候
    print("count:",count)
    count=count+1

2.猜年龄游戏,每个人允许猜3次，如果猜对直接退出

count = 0
age_of_oldboy = 56
while True:  #条件3次，break
    if count ==3:
        break
    guess_age = int(input("guess age:"))
    if guess_age ==age_of_oldboy:
        print("yes,you got it.")
        break                    #条件成立时直接break跳过
    elif guess_age > age_of_oldboy:
        print("think smaller...")
    else:
        print("think bigger!")
        count+=1   #count计数放在最末尾，每个循环执行1次,count+1

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3、略优化上述循环，使用while count 小于3 与if count ==3 break 执行结果一致

count = 0
age_of_oldboy = 56
while count<3:  #while count 小于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("think bigger!")
        count+=1

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4、输入错误答案3次后，需要提示用户不能尝试了

count = 0
age_of_oldboy = 56
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("think bigger!")
        count+=1
else:    #末尾增加判断语句
    print("you have tried too many times..fuck off")

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5、任性玩游戏，当3次跑完后，询问是否继续玩游戏，输入n代表结束，输入任何其他数代表继续

count = 0
age_of_oldboy = 56
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("think bigger!")
    count +=1
    if count ==3:
        countine_confirm = input("do you want to keep guessing..?")
        if countine_confirm != "n":
            count = 0

else:
    print("you have tried too many times..fuck off")

break的意思

break可以理解为破坏的意思，当条件成立执行break后，后面的条件不会在执行。
简单点说，break就是结束整个循环的意思。

for循环

1、简单的for使用方法

for i in range(10): #i为临时变量，递增循环10次，每次+1
    print("loop",i)

2、使用步长为2，打印10以内的偶数

步长默认为1，可以为2，或者3…

for i in range(0,10,2):  #0~10，2代表跳着打印（步长为2）
    print("loop",i)

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3、用for循环执行上段猜年龄游戏

age_of_oldboy = 56
for i in range(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("think bigger!")
else:  #正常走完for循环才会执行else,如果if guess_age == age_of_oldboy成立 执行break，不执行else
    print("you have tried too many times..fuck off")

4、双层循环

每个大循环执行1次，小循环就得执行10次

for i in range(10):
    print('-------------',i)
    for j in range(10):
        print(j)

continue用法

1、continue意思：跳出本次循环，继续到下一次循环。

for i in range(0,10):
    if i <3:
        print("loop",i)
    else:
        continue
    print("hahaha...")

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2、pycharm打断点调试

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插入一个if else 简单判断，当输入用户账号密码登录，使用if else判断

import getpass
_username = "josh"
_password = "josh123"
username = input("username:")
#password = getpass.getpass("password:")
password = input("password:")

if _username == username and _password == password:
    print("Welcome user {name} login...".format(name=username))
else:
    print("Invalid username or password!")