pybind11 very simple example: importError when importing in python

Question

I'm trying to compile a very simple example using pybind11, but unlike all tutorials I can find, I don't want to copy the pybind11 repo into my project. I currently have

CMakeLists.txt

cmake_minimum_required(VERSION 3.22)

project(relativity)

set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED YES)

find_package(pybind11)

file(GLOB SOURCES "*.cpp")

pybind11_add_module(${PROJECT_NAME} ${SOURCES})

main.cpp

#include <pybind11/pybind11.h>

namespace py = pybind11;

int add(int i, int j) {
    return i + j;
}

PYBIND11_MODULE(example, m) {
    m.doc() = "pybind11 example plugin"; // optional module docstring

    m.def("add", &add, "A function that adds two numbers");
}

When I run cmake .. and make I get no errors and the relativity.so file is built. However if I attempt to import it in python using import relativity I get:

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

What am I doing wrong exactly? I can't really find any detailed examples or tutorials that do it this way.

EDIT: I tried cloning the pybind11 repo into my project and using the following CMakeLists.txt

cmake_minimum_required(VERSION 3.22)

project(relativity)

add_subdirectory(pybind11)

pybind11_add_module(${PROJECT_NAME} main.cpp)

but this gives the same error when importing in python3.

lr1985 · Accepted Answer · 2022-07-06 08:59:22Z

2

The first argument passed to the PYBIND11_MODULE macro should be the name of the module (and therefore should match the content of the "PROJECT_NAME" variable as defined in the cmake file):

PYBIND11_MODULE(relativity, m) { // <---- "relativity" instead of "example"
    m.doc() = "pybind11 example plugin"; // optional module docstring

    m.def("add", &add, "A function that adds two numbers");
}

answered Jul 6, 2022 at 8:59

lr1985

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