Python判断字符串是否以字母开头

import re
rule = re.compile('^[a-zA-z]{1}.*$')
str='123'
if rule.match(str) is None:
    print(str+'不以字母开头')
else:
    print(str+'以字母开头')

str2='a12'
if rule.match(str2) is None:
    print(str2+'不以字母开头')
else:
    print(str2+'以字母开头')