while循环

基础循环：

　　while 条件：

　　缩进 循环体

i=1
j=1
while i in range(1,10):
    while j in range(1,i+1):
        print(j,"*",i,"=",j*i,end=' ')
        j += 1
    print()
    i += 1
    j = 1
循环标识位：通过对标识位重新赋值退出循环

flag = True
while flag:#标识位为真，循环进行
    print(flag)
    flag = False #标识位重新赋值为假，结束循环

break关键字

　　用于中断循环，通常在满足某种条件时使用

while flag:#标识位为真，循环进行
    print(flag)
    flag = False #标识位重新赋值为假，结束循环

continue关键字

　　用于结束本次循环，仅仅跳出本次

i = 0
while i in range(10):
    if i == 5:
        continue #当i=5时结束循环
    print(i)
    i += 1
--------
嵌套循环跳出

flag = False
for i in range(10):
    if i < 5 :
        continue
    print(i)
    for j in range(10):
        if j > 5:
            flag = True
            break    #跳出当前循环
        print("Leve %s"%j)
    if flag == True:
        break   #跳出外层循环

while else使用

1，while 条件满足不执行else情况：使用关键字break中止循环

i = 0
while i < 10:
    print(i)
    i += 1
    break
else:
    print("Game over ！")

2，while条件不满足执行else:

i = 0
while i > 10:
    print(i)
    i += 1
    break
else:
    print("Game over ！")

3,while条件满足，while和else均执行：

i = 0
while i < 10:
    print(i)
    i += 1
else:
    print("Game over ！")

九九乘法表

while版

i = 1
j = 1
while i in range(1,10):
    while j in range(1,i+1):
        print(j,"*",i,"=",i*j,end="	")
        j += 1
    print()
    i += 1
    j = 1
for循环版：

for i in range(1,10):
    for j in range(1,i+1):
        print(j,"*",i,"=",j*i,end="	")
        j += 1
    i += 1
    print()

-------------------
登录设计

_user ="zhang"
_passwd = "123456"
counter = 0
while counter <3:
    username = input("Username:")
    password = input("Password:")
    if username == _user and password == _passwd :
        print("Welcome %s login...." % _user)
        break #跳出，中断
    else:
        print("Invalid username or password !")
    counter += 1
    if counter == 3:
        keep_going_choice = input("还想玩么?[y/n]")
        if keep_going_choice == "y":
            counter = 0

else:
    print("退出。")