Python Library Made With Pybind11 From Go Code Throwing ImportError: Dynamic Module Does Not Define Module Export Function

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Resolving ImportError: Dynamic Module Does Not Define Module Export Function in Pybind11

In this article, we will explore the issue of ImportError: dynamic module does not define module export function when creating a Python library using pybind11 from Go code. We will walk through the steps to resolve this issue and provide a comprehensive solution.

You are trying to create a simple Python library that runs Go code through pybind11 and CMake. You have installed pybind11 through Anaconda in a virtual environment (venv) named goscrapper. Your IDE is VSCode. However, when you try to run your Python library, you encounter the following error:

ImportError: dynamic module does not define module export function

Here are the steps you have taken so far:

Step 1: Create a New CMake Project

You created a new CMake project using the following command:

mkdir goscrapper
cd goscrapper

Step 2: Install pybind11

You installed pybind11 through Anaconda in your virtual environment (venv) using the following command:

conda create -n goscrapper python pybind11
conda activate goscrapper

Step 3: Write Go Code

You wrote a simple Go code that you want to run through pybind11. Let's assume the Go code is in a file named goscrapper.go.

Step 4: Create a C++ Wrapper

You created a C++ wrapper using pybind11 to call the Go code. Let's assume the C++ wrapper is in a file named goscrapper.cpp.

Step 5: Create a CMakeLists.txt File

You created a CMakeLists.txt file to build your C++ wrapper and link it with pybind11.

Step 6: Build and Run the Python Library

You built and ran your Python library using the following commands:

cmake .
cmake --build .
python goscrapper.py

However, when you run the Python library, you encounter the following error:

ImportError: dynamic module does not define module export function

To resolve the issue, we need to understand what is causing the error. The error message indicates that the dynamic module (i.e., the shared library generated by CMake) does not define a module export function.

In pybind11, the module export function is defined using the PYBIND11_MODULE macro. However, in your C++ wrapper, you may have forgotten to define this macro.

Here is an example of how to define the module export function using pybind11:

#include <pybind11/pybind11.h>

namespace py = pybind11;


PYBIND11_MODULE(goscrapper, m) {
// Define the module export function
m.def("goscrapper", &goscrapper);
}

In this example, we define a module export function named goscrapper using the PYBIND11_MODULE macro. The goscrapper function is defined in the goscrapper.cpp file.

To fix the issue, you need to add the PYBIND11_MODULE macro to your C++ wrapper and define the module export function.

Here is the complete solution:

Step 1: Update the C++ Wrapper

Update the goscrapper.cpp file to include the PYBIND11_MODULE macro:

#include <pybind11/pybind11.h>

namespace py = pybind11;


PYBIND11_MODULE(goscrapper, m) {
// Define the module export function
m.def("goscrapper", &goscrapper);
}

Step 2: Update the CMakeLists.txt File

Update the CMakeLists.txt file to include the PYBIND11_MODULE macro:

cmake_minimum_required(VERSION 3.10)
project(goscrapper)

find_package(pybind11 REQUIRED)


add_library(goscrapper SHARED goscrapper.cpp)
target_link_libraries(goscrapper pybind11::pybind11)

Step 3: Rebuild and Run the Python Library

Rebuild and run the Python library using the following commands:

cmake .
cmake --build .
python goscrapper.py

This should resolve the issue and allow you to run your Python library successfully.

In this article, we explored the issue of ImportError: dynamic module does not define module export function when creating a Python library using pybind11 from Go code. We walked through the steps to resolve this issue and provided a comprehensive solution. By following these steps, you should be able to create a Python library that runs Go code through pybind11 and CMake successfully.
Frequently Asked Questions (FAQs) - Resolving ImportError: Dynamic Module Does Not Define Module Export Function in Pybind11

A: The cause of this error is that the dynamic module (i.e., the shared library generated by CMake) does not define a module export function. In pybind11, the module export function is defined using the PYBIND11_MODULE macro.

A: The PYBIND11_MODULE macro is used to define a module export function in pybind11. It takes two arguments: the name of the module and a reference to the module object. The module object is used to define the functions and variables that will be exported by the module.

A: To define a module export function using the PYBIND11_MODULE macro, you need to include the pybind11 header file and define the module export function using the PYBIND11_MODULE macro. Here is an example:

#include <pybind11/pybind11.h>

namespace py = pybind11;


PYBIND11_MODULE(goscrapper, m) {
// Define the module export function
m.def("goscrapper", &goscrapper);
}

A: A module export function is a special type of function that is defined using the PYBIND11_MODULE macro. It is used to export functions and variables from a shared library to Python. A regular function is a function that is defined using the def keyword in Python.

A: To know if you have defined a module export function correctly, you can check the following:

  • Make sure you have included the pybind11 header file.
  • Make sure you have defined the module export function using the PYBIND11_MODULE macro.
  • Make sure the module export function is correctly defined and exported.

A: Some common mistakes that can cause this error include:

  • Forgetting to include the pybind11 header file.
  • Forgetting to define the module export function using the PYBIND11_MODULE macro.
  • Defining the module export function incorrectly.
  • Not exporting the functions and variables correctly.

A: To troubleshoot this error, you can try the following:

  • Check the CMakeLists.txt file to make sure it is correctly configured.
  • Check the pybind11 documentation to make sure you are using the correct syntax.
  • Check the shared library generated by CMake to make sure it is correctly exported.
  • Use the pybind11 command-line tool to debug the shared library.

A: Yes, you can use pybind11 with other C++ libraries. Pybind11 is designed to be flexible and can be used with a wide range of C++ libraries.

A: Pybind11 is compatible with Python 3.6 and later versions. However, it may not be compatible with all versions of Python, so be sure to check the pybind11 documentation for the latest information.

A: Yes, you can use pybind11 with other programming languages. Pybind11 is designed to be flexible and can be used with a wide range of programming languages.