I found a great post by Adrian Rosebrock for how to install OpenCV on Ubuntu 18.04 and for the cmake command I was able to build it using Anaconda

cmake_cmmd.sh

cmake -D CMAKE_BUILD_TYPE=RELEASE \
      -D CMAKE_INSTALL_PREFIX=/usr/local \
      -D INSTALL_PYTHON_EXAMPLES=ON \
      -D INSTALL_C_EXAMPLES=OFF \
      -D OPENCV_EXTRA_MODULES_PATH='~/Downloads/opencv/opencv_contrib-3.4.2/modules/' \
      -D PYTHON3_INCLUDE_DIR='~/anaconda3/envs/tf/include/python3.6m' \
      -D PYTHON_EXECUTABLE='~/anaconda3/envs/tf/bin/python' \
      -D PYTHON3_LIBRARY='~/anaconda3/envs/tf/lib/libpython3.6m.so' \
      -D PYTHON3_PACKAGES_PATH='~/anaconda3/envs/tf/lib/python3.6/site-packages' \
      -D PYTHON3_NUMPY_INCLUDE_DIRS='~/anaconda3/envs/tf/lib/python3.6/site-packages/numpy/core/include' \
      -D BUILD_EXAMPLES=ON -D BUILD_NEW_PYTHON_SUPPORT=ON ..

Adrian Rosebrock great guide

Hope this will help.

BTW thanks Adrian

Hello @zeroows,
I'm trying to install opencv for anaconda python 3.6.
I was able to complete 4 steps of Adrian's guide but I'm unable to find the cv2.cpython-36m-x86_64-linux-gnu.so file
in anaconda3/lib/python3.6/site-packages. Can you help?