I wasted 2 hours on building OpenCV 4.2.0 from source on Apple M1 Pro with Python3.8 bindings. Here are the steps if anyone else is stuck on this. I am on Mac OS Mojave btw.

Note: Don’t waste your time with Pyenv. Too much goes wrong with it, stick to /usr/bin/python3 (system install python3). In my case this was Python 3.8.9

Virtualenv

Start by creating virtualenv with the new bundled in venv module. Simple enough

mkdir ~/.virtualenvs
# calling my env gurus because I am trying to get through pyimagesearch gurus course
/usr/bin/python3 -m venv ~/.virtualenvs/gurus 

Dependencies from Homebrew

brew update
brew install wget cmake jpeg libpng libtiff openexr eigen tbb

Install numpy

source ~/.virtualenvs/gurus/bin/activate
pip install numpy

Download and build OpenCV 4.2.0

wget -O opencv.zip https://github.com/opencv/opencv/archive/4.2.0.zip
wget -O opencv_contrib.zip https://github.com/opencv/opencv_contrib/archive/4.2.0.zip
unzip opencv-4.2.0.zip
unzip opencv_contrib.zip
mv opencv-4.2.0 opencv
mv opencv_contrib-4.2.0 opencv_contrib
cd ~/opencv
mkdir build && cd build
source ~/.virtualenvs/gurus/bin/activate

Okay so this is where all my time went. python-config doesn’t have the option of --configdir any more. So if you need to find out where the libpython3.8.dylib is located, you have to play by the new rules. Head to python3 shell

import distutils.sysconfig as s
print(s.get_python_inc())

This will very likely lead to something like: /Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/include/python3.8

Well, the dylib is at /Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/libpython3.8.dylib.

Best to verify it yourself. This path is going to be used for our CMAKE command when configuring OpenCV. Particularly the variable PYTHON3_LIBRARY

So, now we continue with our configuration process. Within the build directory

cmake -D CMAKE_BUILD_TYPE=RELEASE \
    -D CMAKE_INSTALL_PREFIX=/usr/local \
    -D OPENCV_EXTRA_MODULES_PATH=~/opencv_contrib/modules \
    -D PYTHON3_LIBRARY=‘/Library/Developer/CommandLineTools/Library/Frameworks/Python3.framework/Versions/3.8/lib/libpython3.8.dylib’ \
    -D PYTHON3_INCLUDE_DIR=`python -c 'import distutils.sysconfig as s; print(s.get_python_inc())'` \
    -D PYTHON3_EXECUTABLE=$VIRTUAL_ENV/bin/python \
    -D BUILD_opencv_python2=OFF \
    -D BUILD_opencv_python3=ON \
    -D INSTALL_PYTHON_EXAMPLES=ON \
    -D INSTALL_C_EXAMPLES=OFF \
    -D OPENCV_ENABLE_NONFREE=ON \
    -D BUILD_EXAMPLES=ON ..

Which will yield a lot of config stuff. Then simply build it.

make -j4
sudo make install

Symlink

Once it has been built and installed, simply go ahead and find out where the cv2.cpython file was spit out.

mdfind cv2.cpython

In my case I saw it installed here:

/usr/local/lib/python3.8/site-packages/cv2/python-3.8/cv2.cpython-38-darwin.so

Sweet, now let’s symlink it in our site-packages. To locate that you can call get_python_lib() with distutils sysconfig

import distutils.sysconfig as s
s.get_python_lib()

Head to site-packages and simply link the cv2.python

cd '/Users/<your user>/.virtualenvs/gurus/lib/python3.8/site-packages'
ln -s /usr/local/lib/python3.8/site-packages/cv2/python-3.8/cv2.cpython-38-darwin.so

Test

source ~/.virtualenvs/gurus/bin/activate
python3 -c "import cv2; print(cv2.__version__)"
# 4.2.0

That’s it. Now I can actually get to the learning bit.

Also, hooray! First and last post of 2023 \o/