以写代学：python 数据类型之字符串，判断用户输入的id是否符合要求

字符串操作符

比较操作符：字符串大小按ASCLL码值大小进行比较

切片操作符：[]、[:]、[::]

成员关系操作符：in、not in

脚本：判断用户输入的id是否符合要求

#!/usr/bin/env python

import string

#定义字符的范围
first_id = string.letters + "_"           //确定首字符的范围
all_id = string.digits + first_id         //确定其他字符的范围

#请求用户输入id
myid = raw_input("input your id: ")   //请求用户输入id

#判断id是否合法
if len(myid) < 2:   
    print " you must input id longer then 2. "
else:
    if myid[0] not in first_id:
        print "first char %s is invalid" % (myid[0])
    else:
        for ch in myid[1:]:
            if ch not in all_id:
                print "other char invalid"
                break
        else:
            print "%s is valid" % (myid)

以下将判断写成了函数，可以调用

#!/usr/bin/env python

import string

first_chr = string.letters + "_"
all_chr = first_chr + string.digits

myid = raw_input("input your id: ")

def id_check(myid):
    if len(myid) < 2:
        print "you must input char longer than 2. "
    else:
        if myid[0] not in first_chr:
            print "your first char is invalid"
        else:
            for i in range(len(myid[1:])):
                ind = i + 1
                if myid[ind] not in all_chr:
                    print "char is invalid in position %s" % ind
            else:
                print "your id is valid"

if __name__  == "__main__":
    id_check("123")
    id_check("abc")