实例（Python2.x） - 使用 while 循环

#!/usr/bin/python

# -*- coding: UTF-8 -*- 

import string

s = raw_input('请输入一个字符串:\n')

letters = 0

space = 0

digit = 0

others = 0

i=0

while i < len(s):

    c = s[i]

   i += 1

   if c.isalpha():

        letters += 1

   elif c.isspace():

        space += 1

   elif c.isdigit():

        digit += 1

   else:

        others += 1

print 'char = %d,space = %d,digit = %d,others = %d' % (letters,space,digit,others)