Pybind11: Import Error: dynamic module does not define module export function

[nyckmaia]

I had a working Pybind11 Module called maialib and I decided to split it in two files to get a better organization and reduce compile time.

To do that, I following this tutorial here:
https://pybind11.readthedocs.io/en/stable/faq.html#how-can-i-reduce-the-build-time

So, after that, my C++ code still compiles without any error! All ok!

Scanning dependencies of target maialib
[ 25%] Building CXX object CMakeFiles/maialib.dir/src/pugixml.cpp.o
[ 50%] Building CXX object CMakeFiles/maialib.dir/src/functions.cpp.o
[ 75%] Building CXX object CMakeFiles/maialib.dir/src/musicxml.cpp.o
[100%] Linking CXX shared module maialib.cpython-37m-darwin.so
[100%] Built target maialib

But when I tried to import maialib in the Python environment, I got this run-time error:

ImportError: dynamic module does not define module export function (PyInit_maialib)

Here is my CMakeLists.txt:

# Generate python module library
if(PYBIND_LIB)
    message("=====> GENERATING PYBIND LIBRARY <=====")

    add_definitions(-DPYBIND)

    find_package(PythonLibs)
    include_directories(${PYTHON_INCLUDE_DIRS})

    add_subdirectory(pybind11)
    pybind11_add_module(maialib src/pugixml.cpp src/functions.cpp src/musicxml.cpp)
    target_include_directories(maialib PUBLIC include)
endif()

Here is my maialib.h:

// maialib.h

#include <pybind11/pybind11.h>

namespace py = pybind11;

void MusicXMLClass(py::module &);
void functions(py::module &);

PYBIND11_MODULE(maialib, m) {

    m.doc() = "This is a Python binding of C++ Maia Library";

    MusicXMLClass(m);
    functions(m);
}

• The output file name is identical: maialib
• I'm only using Python 3.7

How can I fix this Python run-time error?

[hmageste]

Same problem for me. I was following the tutorial for compiling with CMake.

I am using the latest version of Visual Studio 2017, which is 15.9.21. And Python 3.7.6 shipped with Anaconda.

[carlsonmark]

Have you tried putting this code in a .cpp file instead of a header file?

PYBIND11_MODULE(maialib, m) {

    m.doc() = "This is a Python binding of C++ Maia Library";

    MusicXMLClass(m);
    functions(m);
}

[nyckmaia]

Perfect @carlsonmark !

The main PYBIND11_MODULE MUST BE inside a *.cpp file.
Now it works good!

Thank you again!