如何使用正则表达式匹配恰好三个连续数字？

(?<!d)(d{3})(?!d)

import redata = [    '123',    '123u',    'u123',    'x123y',    '1234',    'x1234y',    '12',    '123y456',]for s in data:    print(re.findall(r'(?<!d)(d{3})(?!d)', s))

['123']['123']['123']['123'][][][]['123', '456']