Missing config-3.py and config-3.8.py during installation from source


I’m messing up when trying to install openCV from sources.

System: Ubuntu 18.04
OpenCV Version: 4.5.2 (latest)
Python: Python 3.8 and 3.9 (via anaconda)

Tutorial followed - How to install OpenCV 4.2 with CUDA 10.0 in Ubuntu 18.04 · GitHub

I’ve followed above tutorial, using anaconda python.

    Isaac@MSI:~/opencv-4.5.2/build/python_loader$ python setup.py install
    running install
    running bdist_egg
    running egg_info
    writing opencv.egg-info/PKG-INFO
    writing dependency_links to opencv.egg-info/dependency_links.txt
    writing requirements to opencv.egg-info/requires.txt
    writing top-level names to opencv.egg-info/top_level.txt
    reading manifest file 'opencv.egg-info/SOURCES.txt'
    writing manifest file 'opencv.egg-info/SOURCES.txt'
    installing library code to build/bdist.linux-x86_64/egg
    running install_lib
    running build_py
    creating build/bdist.linux-x86_64/egg
    creating build/bdist.linux-x86_64/egg/cv2
    copying build/lib/cv2/load_config_py2.py -> build/bdist.linux-x86_64/egg/cv2
    copying build/lib/cv2/config.py -> build/bdist.linux-x86_64/egg/cv2
    copying build/lib/cv2/load_config_py3.py -> build/bdist.linux-x86_64/egg/cv2
    copying build/lib/cv2/__init__.py -> build/bdist.linux-x86_64/egg/cv2
    byte-compiling build/bdist.linux-x86_64/egg/cv2/load_config_py2.py to load_config_py2.cpython-39.pyc
    byte-compiling build/bdist.linux-x86_64/egg/cv2/config.py to config.cpython-39.pyc
    byte-compiling build/bdist.linux-x86_64/egg/cv2/load_config_py3.py to load_config_py3.cpython-39.pyc
    byte-compiling build/bdist.linux-x86_64/egg/cv2/__init__.py to __init__.cpython-39.pyc
    creating build/bdist.linux-x86_64/egg/EGG-INFO
    copying opencv.egg-info/PKG-INFO -> build/bdist.linux-x86_64/egg/EGG-INFO
    copying opencv.egg-info/SOURCES.txt -> build/bdist.linux-x86_64/egg/EGG-INFO
    copying opencv.egg-info/dependency_links.txt -> build/bdist.linux-x86_64/egg/EGG-INFO
    copying opencv.egg-info/requires.txt -> build/bdist.linux-x86_64/egg/EGG-INFO
    copying opencv.egg-info/top_level.txt -> build/bdist.linux-x86_64/egg/EGG-INFO
    zip_safe flag not set; analyzing archive contents...
    cv2.__pycache__.__init__.cpython-39: module references __file__
    creating 'dist/opencv-4.5.2-py3.9.egg' and adding 'build/bdist.linux-x86_64/egg' to it
    removing 'build/bdist.linux-x86_64/egg' (and everything under it)
    Processing opencv-4.5.2-py3.9.egg
    removing '/home/isaac/anaconda3/envs/cv/lib/python3.9/site-packages/opencv-4.5.2-py3.9.egg' (and everything under it)
    creating /home/isaac/anaconda3/envs/cv/lib/python3.9/site-packages/opencv-4.5.2-py3.9.egg
    Extracting opencv-4.5.2-py3.9.egg to /home/isaac/anaconda3/envs/cv/lib/python3.9/site-packages
    opencv 4.5.2 is already the active version in easy-install.pth

    Installed /home/isaac/anaconda3/envs/cv/lib/python3.9/site-packages/opencv-4.5.2-py3.9.egg
    Processing dependencies for opencv==4.5.2
    Searching for numpy==1.20.1
    Best match: numpy 1.20.1
    Adding numpy 1.20.1 to easy-install.pth file
    Installing f2py script to /home/isaac/anaconda3/envs/cv/bin
    Installing f2py3 script to /home/isaac/anaconda3/envs/cv/bin
    Installing f2py3.9 script to /home/isaac/anaconda3/envs/cv/bin

    Using /home/isaac/anaconda3/envs/cv/lib/python3.9/site-packages
    Finished processing dependencies for opencv==4.5.2

But when trying to import cv2 and check that everything works, this error arrise:

    (cv) isaac@MSI:~/opencv-4.5.2/build/python_loader$ python
    Python 3.9.4 (default, Apr  9 2021, 16:34:09)
    [GCC 7.3.0] :: Anaconda, Inc. on linux
    Type "help", "copyright", "credits" or "license" for more information.
    >>> import cv2
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "/home/isaac/opencv-4.5.2/build/python_loader/cv2/__init__.py", line 102, in <module>
      File "/home/isaac/opencv-4.5.2/build/python_loader/cv2/__init__.py", line 63, in bootstrap
      File "/home/isaac/opencv-4.5.2/build/python_loader/cv2/__init__.py", line 60, in load_first_config
        raise ImportError('OpenCV loader: missing configuration file: {}. Check OpenCV installation.'.format(fnames))
    ImportError: OpenCV loader: missing configuration file: ['config-3.9.py', 'config-3.py']. Check OpenCV installation.
    >>> exit()

I’ve not found so many discussions with config-3.py or any other variant related with the lines above. I’ve just found the solution of using pip install --upgrade opencv-python which was something I was trying to avoid

Am I missing sth? Is there a way to debug the line 60 error and not install opencv-pyhton


I would recommend discarding that “tutorial”.

ignore anything that has superfluous steps, such as a python virtualenv, or installing a ton of random libraries you might not even need.

work with official documentation.


  • get the sources (git clone, checkout a version tag)
  • start cmake or cmake-gui
  • cmake: configure until it works, disable modules that cause trouble
  • cmake: generate build files
  • build (make)
  • install, maybe

Thanks for your reply. I’ll try to do it again from scratch… but the cmake and build process of openCV is still a pass in the tutorial… and is where I’m getting stuck. I don’t think the problem come from installing libraries which might be also related with CUDA.

I’ll do it again, but I would appreciate knowing which are the cmake parameters to generate this config-3.9.py or config-3.py files
And also, the purpose of them… as I haven’t found the answer by myself

Same problem here:

OpenCV loader: missing configuration file: ['config-3.9.py', 'config-3.py']. Check OpenCV installation.

  File "C:\OpenCV\OpenCV_build\python_loader\cv2\__init__.py", line 109, in load_first_config
    raise ImportError('OpenCV loader: missing configuration file: {}. Check OpenCV installation.'.format(fnames))
  File "C:\OpenCV\OpenCV_build\python_loader\cv2\__init__.py", line 112, in bootstrap
  File "C:\OpenCV\OpenCV_build\python_loader\cv2\__init__.py", line 181, in <module> (Current frame)

I have no idea, why it is not acepting Python3.9