测试python合法标识符的函数

#!/usr/bin/env python
#filename:is_id.py
#development environment:python2.51

from string import *
from keyword import kwlist
def is_id(string):
    alphas=letters+'_'
    nums=digits
    if len(string)==1 and string in alphas:
        return True
    elif len(string)>1:
        if string[0] not in alphas or (string in kwlist):
            return False
        else:
            for i in string[1:]:
                if i not in alphas+nums:
                    return False
                else:
                    return True