Mac El Capitan系统Python2.7安装OpenCV后cv2导入报错解决方法

Hey there, let's tackle that annoying import error you're facing. The root of the problem is straightforward: Mac OS X 10.11 El Capitan doesn't include the _clock_gettime system symbol, but the pre-built opencv-python wheels from PyPI are compiled for newer macOS versions that do have this function. Here are two reliable ways to fix it:

Method 1: Use Homebrew to Install a Compatible OpenCV Version #

This is the quickest fix if it works for your setup:

1. Clean up all existing OpenCV installations first to avoid conflicts:

   • Uninstall the PyPI version:

     pip uninstall -y opencv-python
     

   • Force-uninstall any Homebrew OpenCV versions:

     brew uninstall --force opencv
     

   • Delete leftover cv2 files from your Python site-packages:

     rm -rf /Library/Python/2.7/site-packages/cv2
     

2. Install a legacy OpenCV version compatible with El Capitan
   OpenCV 3.x is the last major release that supports Python 2.7, and Homebrew has a dedicated formula for it:

   brew install opencv@3
   

3. Link OpenCV's Python bindings to your system Python 2.7
   First, get the installation path of opencv@3:

   brew --prefix opencv@3
   

   (This should output something like /usr/local/opt/opencv@3)

   Then create a symbolic link to connect the OpenCV bindings to your Python's site-packages:

   ln -s /usr/local/opt/opencv@3/lib/python2.7/site-packages/cv2 /Library/Python/2.7/site-packages/cv2
   

   Finally, add OpenCV's library path to your system so Python can find it:

   echo /usr/local/opt/opencv@3/lib >> /etc/paths.d/opencv3
   

4. Test the installation
   Open a Python 2.7 shell and run:

   import cv2
   print(cv2.__version__)
   

   If you see the version number (like 3.4.x), you're good to go!

Method 2: Compile OpenCV from Source (For Full Control) #

If the Homebrew method doesn't work, compiling from source guarantees compatibility with El Capitan:

1. Install build dependencies

   brew install cmake pkg-config numpy
   

2. Clean up existing installations (same as step 1 in Method 1)

   pip uninstall -y opencv-python
   brew uninstall --force opencv
   rm -rf /Library/Python/2.7/site-packages/cv2
   

3. Clone the correct OpenCV source versions
   We'll use OpenCV 3.4.16, the final release that supports Python 2.7:

   # Clone OpenCV main repo
   git clone https://github.com/opencv/opencv.git
   cd opencv
   git checkout 3.4.16
   
   # Clone the extra modules repo (matches the main version)
   git clone https://github.com/opencv/opencv_contrib.git ../opencv_contrib
   cd ../opencv_contrib
   git checkout 3.4.16
   

4. Configure the build with CMake
   Create a build directory and run CMake with Python 2.7-specific settings:

   cd ../opencv
   mkdir build
   cd build
   
   cmake -D CMAKE_BUILD_TYPE=RELEASE \
         -D CMAKE_INSTALL_PREFIX=/usr/local \
         -D OPENCV_EXTRA_MODULES_PATH=../../opencv_contrib/modules \
         -D PYTHON2_EXECUTABLE=/usr/bin/python \
         -D PYTHON2_INCLUDE_DIR=/usr/include/python2.7 \
         -D PYTHON2_LIBRARY=/usr/lib/libpython2.7.dylib \
         -D PYTHON2_NUMPY_INCLUDE_DIRS=/Library/Python/2.7/site-packages/numpy/core/include \
         -D BUILD_opencv_python2=ON \
         -D BUILD_opencv_python3=OFF \
         -D WITH_FFMPEG=OFF \
         ..
   

5. Compile and install
   Use the -j flag with the number of CPU cores you have (e.g., -j4 for 4 cores) to speed up compilation:

   make -j4
   sudo make install
   

6. Test the installation
   Run this command to verify:

   python -c "import cv2; print(cv2.__version__)"
   

A quick note: Python 2.7 is no longer supported by the Python Software Foundation, so if you can, consider migrating to Python 3 for long-term stability. But if you need to stick with 2.7, either of these methods should resolve the _clock_gettime error.

内容的提问来源于stack exchange，提问作者marc