代码

import re

p = re.compile(r'(\d+)-(\d+)-(\d+)')
print(p.match('2018-05-10').group(2))
print(p.match('2018-05-10').groups())
print(p.search('aaaaa2018-05-10'))
print(p.search('aaaaa20aaa18-05-10'))
print(p.search('aaaaa20aaa18aa-05-10'))

运行