最后安装requests，因为它对前四个有依赖
pip install certifi-2020.12.5-py2.py3-none-any.whl pip install chardet-4.0.0-py2.py3-none-any.whl pip install idna-2.5-py2.py3-none-any.whl pip install urllib3-1.26.4-py2.py3-none-any.whl pip install requests-2.25.1-py2.py3-none-any.whl
python包的下载地址 https://pypi.org/project/PyMySQL/#files