错误：无法为使用 PEP 517 且无法直接安装的 opencv-python 构建轮子（在 PATH 中找不到 cl）答案

【问题标题】：ERROR: Could not build wheels for opencv-python which use PEP 517 and cannot be installed directly (cl was not found in PATH)错误：无法为使用 PEP 517 且无法直接安装的 opencv-python 构建轮子（在 PATH 中找不到 cl）
【发布时间】：2021-01-30 01:04:11
【问题描述】：

我试图在 Visual Studio 中安装 opencv-python（安装了 Visual Studio 2019），但一直出现此错误。我已经尝试了之前发布的有关此 PEP517 错误的大多数方法，但我仍然遇到错误。感谢有人可以在这里帮助我，因为我只是一个初学者编码器。非常感谢。

以下是错误代码：

$ pip install opencv-python
Collecting opencv-python
  Using cached opencv-python-4.4.0.44.tar.gz (88.9 MB)
  Installing build dependencies ... done
  Getting requirements to build wheel ... done
    Preparing wheel metadata ... done
Requirement already satisfied: numpy>=1.17.3 in c:\python\lib\site-packages (from opencv-python) (1.19.2)
Building wheels for collected packages: opencv-python
  Building wheel for opencv-python (PEP 517) ... error
  ERROR: Command errored out with exit status 1:
   command: 'c:\python\python.exe' 'c:\python\lib\site-packages\pip\_vendor\pep517\_in_process.py' build_wheel 'C:\Users\Austen\AppData\Local\Temp\tmp6zo4yrsx'
       cwd: C:\Users\Austen\AppData\Local\Temp\pip-install-tcb_5anh\opencv-python
  Complete output (153 lines):
  Not searching for unused variables given on the command line.
  CMake Error: CMake was unable to find a build program corresponding to "Ninja".  CMAKE_MAKE_PROGRAM is not set.  You probably need to select a different build tool.
  -- Configuring incomplete, errors occurred!
  See also "C:/Users/Austen/AppData/Local/Temp/pip-install-tcb_5anh/opencv-python/_cmake_test_compile/build/CMakeFiles/CMakeOutput.log".
  Not searching for unused variables given on the command line.
  CMake Error at CMakeLists.txt:2 (PROJECT):
    Generator

      Visual Studio 15 2017 Win64

    could not find any instance of Visual Studio.


  -- Configuring incomplete, errors occurred!
  See also "C:/Users/Austen/AppData/Local/Temp/pip-install-tcb_5anh/opencv-python/_cmake_test_compile/build/CMakeFiles/CMakeOutput.log".
  Not searching for unused variables given on the command line.
  -- The C compiler identification is unknown
  CMake Error at CMakeLists.txt:3 (ENABLE_LANGUAGE):
    The CMAKE_C_COMPILER:

      cl

    is not a full path and was not found in the PATH.

    To use the NMake generator with Visual C++, cmake must be run from a shell
    that can use the compiler cl from the command line.  This environment is
    unable to invoke the cl compiler.  To fix this problem, run cmake from the
    Visual Studio Command Prompt (vcvarsall.bat).

    Tell CMake where to find the compiler by setting either the environment
    variable "CC" or the CMake cache entry CMAKE_C_COMPILER to the full path to
    the compiler, or to the compiler name if it is in the PATH.

  ********************************************************************************
  ----------------------------------------
  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

【问题讨论】：

您使用的是哪个 Python 版本？过去对于使用哪个编译器构建扩展非常挑剔。
您好，我目前使用的是最新版本的python（v3.9）

标签： python c++ opencv cmake

【解决方案1】：

我已经成功解决了这个错误问题。有两种方法，你可以使用任何一种：

将 Python 3.9 降级到 Python 3.8
使用 conda 代替 pip（如果您安装了 python 3.9 并且不想降级）

干杯！

【讨论】：