CMAKE Could NOT find PythonLibs (missing: PYTHON_INCLUDE_DIRS)

Question

I am trying to run cmake in our school project, the CMakeList.txt looks as follows:

cmake_minimum_required(VERSION 3.0)
project(nagata)
FIND_PACKAGE( OpenMP )
if(OPENMP_FOUND)
message("OPENMP FOUND")
set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} ${OpenMP_C_FLAGS}")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${OpenMP_CXX_FLAGS}")
set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} ${OpenMP_EXE_LINKER_FLAGS}")
endif()

set(CMAKE_C_COMPILER clang-omp CACHE STRING "C compiler" FORCE)
set(CMAKE_CXX_COMPILER clang-omp++ CACHE STRING "C++ compiler" FORCE)

FIND_PACKAGE( pybind11 REQUIRED )

FIND_PACKAGE(PythonInterp 3)
FIND_PACKAGE(PythonLibs   3)

IF( PYTHONINTERP_FOUND AND PYTHONLIBS_FOUND AND PYBIND11_FOUND )
  INCLUDE_DIRECTORIES(
    ${PYTHON_INCLUDE_DIRS}
    ${PYBIND11_INCLUDE_DIRS}
  )
  ENDIF()
INCLUDE_DIRECTORIES("/usr/include/python3.7m")

add_library(pynagata SHARED pythonlib.cpp)
 # The library must not have any prefix and should be located in
  # a subfolder that includes the package name. The setup will be
  # more complicated otherwise.
  SET_TARGET_PROPERTIES( pynagata
    PROPERTIES
      PREFIX ""
      LIBRARY_OUTPUT_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}/pynagata"
  )

add_executable(nagata main.cpp)
install(TARGETS nagata RUNTIME DESTINATION bin)

When I run cmake .. in my build directory I get this output which looks almost OK:

-- The C compiler identification is Clang 11.0.0
-- The CXX compiler identification is Clang 11.0.0
-- Detecting C compiler ABI info
-- Detecting C compiler ABI info - done
-- Check for working C compiler: /usr/local/opt/llvm/bin/clang - skipped
-- Detecting C compile features
-- Detecting C compile features - done
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/local/opt/llvm/bin/clang++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- Found OpenMP_C: -fopenmp=libomp (found version "5.0") 
-- Found OpenMP_CXX: -fopenmp=libomp (found version "5.0") 
-- Found OpenMP: TRUE (found version "5.0")  
OPENMP FOUND
-- Found PythonInterp: /usr/local/bin/python3.8 (found version "3.8.6") 
-- Found PythonLibs: /usr/local/opt/python@3.8/Frameworks/Python.framework/Versions/3.8/lib/libpython3.8.dylib
-- Performing Test HAS_CPP14_FLAG
-- Performing Test HAS_CPP14_FLAG - Success
-- Found PythonInterp: /usr/local/bin/python3.8 (found suitable version "3.8.6", minimum required is "3") 
-- Could NOT find PythonLibs (missing: PYTHON_INCLUDE_DIRS) (Required is at least version "3")
-- Configuring done
-- Generating done
-- Build files have been written to: /Users/.../build

Except the line -- Could NOT find PythonLibs (missing: PYTHON_INCLUDE_DIRS) (Required is at least version "3") which seems odd to me as few lines before it literally finds it: -- Found PythonLibs: /usr/local/opt/python@3.8/Frameworks/Python.framework/Versions/3.8/lib/libpython3.8.dylib . I tried to set an env variable PYTHON_INCLUDE_DIRS="/usr/local/opt/python@3.8/Frameworks/Python.framework/Versions/3.8/lib/libpython3.8.dylib" which is the exact same path as from the line above. Still, I get this error .

How can I make it find the PythonLibs ? I really don't understand why the env variable doesn't work. I will also be happy to provide more info - I just don't know what.

I am using:

• CLT: 12.0.0.0.1.1599194153
• Xcode: 12.0.1
• macOS Catalina ver. 10.15.7
• Clang: 12.0 build 1200

PS: When I try to run make afterwards I get fatal error: 'string' file not found #include <string> which is maybe somehow connected to this issue...

Answer 1

It looks like I got the flags' names wrong. Calling the cmake with the following flags solved the problem for me:

cmake -DPYTHON_LIBRARY=$(python3-config --prefix)/lib/libpython3.8.dylib -DPYTHON_INCLUDE_DIR=$(python3-config --prefix)/include/python3.8 ..

It finds the PythonLibs successfully now.