将.号\号-号的日期格式,全部统一成一种方式
# coding:utf-8
import re
# 目标: 2021-05-28
content = """
白日依2021/05/26山尽,黄河入2021.05.27海流。
欲穷05-28-2020千里目,更上5/29/2020一层楼。
"""
content = re.sub(r"(\d{4})/(\d{2})/(\d{2})", r"\1-\2-\3", content)
content = re.sub(r"(\d{4})\.(\d{2})\.(\d{2})", r"\1-\2-\3", content)
content = re.sub(r"(\d{2})-(\d{2})-(\d{4})", r"\3-\1-\2", content)
content = re.sub(r"(\d{1})/(\d{2})/(\d{4})", r"\3-0\1-\2", content)
print(content)