更新pip为20后不显示下载链接无法离线下载回退pip版本

先看log

WARNING: You are using pip version 19.3.1; however, version 20.0.2 is available.

You should consider upgrading via the 'python -m pip install --upgrade pip' command.

C:\Users\think>python -m pip install --upgrade pip

Collecting pip

Downloading https://files.pythonhosted.org/packages/54/0c/d01aa759fdc501a58f431eb594a17495f15b88da142ce14b5845662c13f3/pip-20.0.2-py2.py3-none-any.whl(1.4MB)

|████████████████████████████████| 1.4MB 16kB/s

Installing collected packages: pip

Found existing installation: pip 19.3.1

Uninstalling pip-19.3.1:

Successfully uninstalled pip-19.3.1

Successfully installed pip-20.0.2

严重的后果：

C:\Users\think>pip3 install imgaug

Collecting imgaug

Using cached imgaug-0.3.0-py2.py3-none-any.whl (819 kB)

Collecting opencv-python-headless

Downloading opencv_python_headless-4.1.2.30-cp37-cp37m-win_amd64.whl (33.0 MB)

没有下载链接，要安装几乎是白日梦。

解决方案：

python -m pip install pip==19.3.1

log如下：

C:\Users\think>python -m pip install pip==19.3.1

Collecting pip==19.3.1

Using cached pip-19.3.1-py2.py3-none-any.whl (1.4 MB)

Installing collected packages: pip

Attempting uninstall: pip

Found existing installation: pip 20.0.2

Uninstalling pip-20.0.2:

Successfully uninstalled pip-20.0.2

Successfully installed pip-19.3.1

重新pip命令安装

C:\Users\think>pip3 install imgaug

Collecting imgaug

Using cached https://files.pythonhosted.org/packages/11/df/5a3bba95b4600d5ca7aff072082ef0d9837056dd28cc4e738e7ce88dd8f8/imgaug-0.3.0-py2.py3-none-any.whl

Requirement already satisfied: scikit-image>=0.14.2 in c:\program files (x86)\microsoft visual studio\shared\python37_64\lib\site-packages (from imgaug) (0.16.2)

Collecting opencv-python-headless

Downloading https://files.pythonhosted.org/packages/38/fa/9268c99a8868f32059a48bb8c2d63e45672e8b4f6c136b8fa6c2c0be94c8/opencv_python_headless-4.1.2.30-cp37-cp37m-win_amd64.whl(33.0MB)

找到链接，迅雷下载后再手动安装既可以