（一）、问题

  通过anaconda prompt安装opencv-python

pip install opencv-python -i http://mirrors.ustc.edu.cn/simple

1、问题：“Could not build wheels for opencv-python which use PEP 517 and cannot be installed directly”

报错原因：

ERROR: Failed building wheel for opencv-python
Failed to build opencv-python
ERROR: Could not build wheels for opencv-python which use PEP 517 and cannot be installed directly

解决办法参考：
①安装opencv时报错：Could not build wheels for opencv-python which use PEP 517 and cannot be installed direc
②Package | 解决 Could not build wheels for opencv-python which use PEP 517 and cannot be installed

我选择的办法是升级pip工具包：

2、问题：“ERROR: Could not install packages due to an EnvironmentError: [WinError 5] 拒绝访问。”

在上一步之后这里仍旧报错，原因如下，没有用户权限，需要在命令后添加“–user”

ERROR: Could not install packages due to an EnvironmentError: [WinError 5] 拒绝访问。: 'C:\\Users\\Arata\\AppData\\Local\\Temp\\pip-uninstall-4med2gjw\\pip.exe'
Consider using the `--user` option or check the permissions.

3、问题：“WARNING: The script wheel.exe is installed in ‘C:\Users\XXX\AppData\Roaming\Python\Python36\Scripts’ which is not on PATH.”

经过上一步已经有有权限下载，但是仍旧报错

报错原因（缺少环境变量）：

 WARNING: The script wheel.exe is installed in 'C:\Users\XXX\AppData\Roaming\Python\Python36\Scripts' which is not on PATH.
 Consider adding this directory to PATH or, if you prefer to suppress this warning, use --no-warn-script-location.

解决办法（新建一个环境变量）：
  我采用的实在系统变量中新建一个，然后将刚开报错的路径加进去，然后重新执行一次下面命令就成功了，如果不行，请重开一个窗口，或者尝试下面链接的办法。

pip install --upgrade pip setuptools wheel -i http://pypi.douban.com/simple/ --user --trusted-host pypi.douban.com

截图演示：

（二）、离线安装

  使用pip语句后安装依旧失败，使用conda安装出现以下提示，那我们进入官网去下载对应版本的离线包,再使用和day1安装torch一样的办法安装，地址“https://anaconda.org”,我还没来得及试一下，就通过第三种方法安装好了

关于Python中使用pip安装库是出现的一个问题

（三）、选择确定版本号后安装

依次输入：

pip install opencv-python==3.4.1.15 -i http://mirrors.aliyun.com/pypi/simple/
pip install opencv-contrib-python==3.4.1.15 -i http://mirrors.aliyun.com/pypi/simple/

以下是安装好的样子：