开始几天的基本学习

#! /usr/bin/env.python
# _*_ coding: utf-8 _*_

    
"""    
start = 1
while True:
    if start == 7:
        start += 1
        continue
    print(start)
    if start == 10:
        break
    start += 1

    
#zheshi  wangshang dashen xiede     
i = 1 
while i < 101:
    print(i)
    i += 1
    if i % 2 == 0:
        i += 1    
    
    

    
    
# zheshi   w ziji  xie de  (1-100shuchu suoyou jishu )    自己写的
start = 1
while True:
    if start%2 == 0:
        start += 1
        continue
    print(start)
    if start == 99:
        break
    start += 1


# zheshi ziji xiede  (1-100shuchusuoyou oushu)
start = 1
while True:
    if start % 2 == 1:
        start += 1
        continue
    print(start)
    if start == 100:
        break
    start += 1

    
start = 1
    print(start)
    if start == 100:
        break
    start += 1
# start = start + 1

#1-100输出奇数
start = 1
while start < 101:
    #如果是奇数， 输出
    #否则不管
    temp = start % 2
    #temp是余数，余数=0.偶数，否则，奇数
    if temp == 1:
        print(start)
    else:
        pass
    start += 1
    
    
#1-100输出 偶数
start = 1
while start < 101:
    temp = start % 2
    if temp == 0:
        print(start)
    else:
        pass
    start += 1

    
#求1-2+3-4+5...99的所有数的和
#思路
#a.1-99所有数的和
start = 1
sum = 0
while start < 100:
    temp = start % 2
    if temp == 1:
        sum = sum + start
    else:
        sum = sum - start
    start += 1
print(sum)


#计算过程 
start = 1
sum = 0
s = ""
while start < 100:
    temp = start % 2
    if temp == 1:
        if start == 1:
            s = str(start)
        else:
            s = s + "+" + str(start) 
        sum = sum + start
    else:
        s = s + "-" + str(start) 
        sum = sum - start
    start += 1
print(s)
print(sum)
"""    
    
#用户登录（三次机会重试）    
#用户登录的实现
#循环三次机会
        #错一次见一次
i = 0
while i < 3:
    user = raw_input("username:")
    pwd = raw_input("password")
    if user == "alex" and pwd == "123":
        print(‘yes‘)
        break
    else:
        print(‘try again‘)
    i += 1