"Could NOT find PythonLibs" in conda environment

Question

CMake can't find my python lib dirs despite being able to find my python executable. As a result, it only builds for my system python2 instead of the python3 for my environment.

-- Found PythonInterp: /usr/bin/python2.7 (found suitable version "2.7.18", minimum required is "2.7") 
-- Found PythonLibs: /home/<user>/.conda/envs/confpaint/lib/libpython3.8.so (found suitable exact version "2.7.18") 
-- Found PythonInterp: /home/<user>/.conda/envs/confpaint/bin/python3 (found suitable version "3.8.6", minimum required is "3.2") 
-- Could NOT find PythonLibs (missing: PYTHON_LIBRARIES PYTHON_INCLUDE_DIRS) (Required is exact version "3.8.6")

...

    --   Python 2:
    --     Interpreter:                 /usr/bin/python2.7 (ver 2.7.18)
    --     Libraries:                   /home/<user>/.conda/envs/confpaint/lib/libpython3.8.so (ver 2.7.18)
    --     numpy:                       /home/<user>/.local/lib/python2.7/site-packages/numpy/core/include (ver 1.14.5)
    --     install path:                lib/python2.7/site-packages/cv2/python-2.7
    -- 
    --   Python (for build):            /home/<user>/.conda/envs/confpaint/bin/python3

Answer 1

You need to specify the location of the include and library dirs to cmake that correspond to your python version. For example, here is what mine looks like:

cmake -DPYTHON3_LIBRARY=/home/<user>/.conda/envs/confpaint/lib/libpython3.8.so \
      -DPYTHON3_INCLUDE_DIRS=/home/<user>/.conda/envs/confpaint/include/python3.8 \
      -DPYTHON_DEFAULT_EXECUTABLE=/home/<user>/.conda/envs/confpaint/bin/python3 ..