Python中exit、return、sys.exit()等使用实例和区别

有这样一道题目：字符串标识符.修改例 6-1 的 idcheck.py 脚本,使之可以检测长度为一的标识符,并且可以识别 Python 关键字,对后一个要求,你可以使用 keyword 模块(特别是 keyword.kelist)来帮你.

我最初的代码是：

#!/usr/bin/env python

import string

import keyword

import sys

#Get all keyword for python

#keyword.kwlist

#['and', 'as', 'assert', 'break', ...]

keyWords = keyword.kwlist

#Get all character for identifier

#string.letters ==> 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'

#string.digits ==> '0123456789'

charForId = string.letters + "_"

numForId = string.digits

idInput = raw_input("Input your words,please!")

if idInput in keyWords:

print "%s is keyword fot Python!" % idInput

else:

lenNum = len(idInput)

if(1 == lenNum):

if(idInput in charForId and idInput != "_"):

print "%s is legal identifier for Python!" % idInput

else:

#It's just "_"

print "%s isn't legal identifier for Python!" % idInput

else:

if(idInput[0:1] in charForId):

legalstring = charForId + numForId

for item in idInput[1:]:

if (item not in legalstring):

print "%s isn't legal identifier for Python!" % idInput

sys.exit(0)

print "%s is legal identifier for Python!2" % idInput

else:

print "%s isn't legal identifier for Python!3" % idInput