s = 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]
if c.isalpha():
letters+=1
elif c.isspace():
space+=1
elif c.isdigit():
digit+=1
else:
others+=1
i+=1
print('letters=%d,space=%d,digit=%d,others=%d' % (letters, space, digit, others))注意点：
1、判断字符串中的某一位是否为字母是调用函数isalpha()，而不是c.isalpha
2、python的格式化输出和C语言类似，用%分隔