python - 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)

Question

我试图在Visual Studio中安装opencv-python(已安装Visual Studio 2019)，但不断出现此错误。我已经尝试过有关此PEP517错误的大多数以前发布的方法，但是我仍然遇到错误。如果我只是一个初学者，请感谢有人可以在这里帮助我。在此先感谢。
下面是错误代码:

$ 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

Answer 1

我已成功解决此错误问题。有两种解决方法，您可以使用其中一种:

将Python 3.9降级为Python 3.8

使用conda而不是pip(如果您已安装python 3.9并且不想降级)

干杯!