1. # 下载
    2. pip download -d ./py_packages requests
    4. # 安装
    5. pip install --no-index --find-links=file:./py_packages requests
    8. ## 安装多个
    9. pip download -d ./py_packages -r requirement.txt
    10. pip install --no-index --find-links=file:./py_packages -r requirement.txt