安装opencv时报错：Could not build wheels for opencv-python which use PEP 517 and cannot be installed direc

一、问题背景

        最近写一批程序，需要用到opencv里面的函数，但是导入cv2的时候，新电脑提示没有安装，所以首先安装opencv的库，直接pip install opencv-python，不过报错了。

        然后从镜像站中安装opencv，直接pip install -i https://mirrors.aliyun.com/pypi/simple opencv-python，不过仍然报错，报错原因和上一次一样：Could not build wheels for opencv-python which use PEP 517 and cannot be installed directly

 二、解决办法

        网上找了很多办法，有的说不要用PEP517，有的说不要用默认的路径，有的说从镜像站下载，我都试过了，没有解决问题。

        后来从stackoverflow上找到类似的问题：c++ - ERROR: Could not build wheels for opencv-python which use PEP 517 and cannot be installed directly (cl was not found in PATH) - Stack Overflow

        回答的建议是：

I have successfully resolved this error issue. There are two methods of going about it, you can use either:

1. Downgrading Python 3.9 to Python 3.8
2. Use conda instead of pip (if you have python 3.9 installed and don't want to downgrade)

Cheers!

        要么把python的版本降低，要么用conda安装。

        我选择用conda安装，具体解决方案如下：

        （1）首先输入conda install opencv-python，不过报错提示没有找到这个库，可以从它的官网去搜索。

         从官网搜索opencv的结果如下：

         （2）安装py-opencv，直接conda install py-opencv就可以了：

        （3）等安装完成，然后import cv2测试一下，成果导入，没有报错，问题解决：