Pybind11 - Multiple definition of PyInit_module_name

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I wrote a library where headers and python bindings are auto-generated. For example dummy_bind.cpp for dummy_message.h and each _bind.cpp file has PYBIND11_MODULE call in it for their specific class. There are dozens of other _bind.cpp files for other headers. What should be the module name for each file when calling the PYBIND11_MODULE like:

PYBIND11_MODULE(protocol_name, m)
{
    /// …
}

If I use protocol_name in each PYBIND11_MODULE(protocol_name, m) call, when compiling I get multiple definition error like: multiple definition of PyInit_protocol_name. If I generate special module name for each message like PYBIND11_MODULE(protocol_name_dummy, m) the extension is compiled but I think I need to import each module one by one which is not viable.

Should I do all exports inside a single PYBIND11_MODULE call? Thanks in advance.

You certainly can't have multiple modules with the same name, you'll need to do something different — Alan Birtles
– Alan Birtles, Commented Feb 25 at 7:13

no more sigsegv · Accepted Answer · 2025-02-25 08:40:17Z

I've actually solved this by generating proxy functions in _bind.cpp files. For instance, in message1_bind.cpp I've defined a function void init_message1(pyinit11::module& m) and then in main_bind.cpp I call them all inside PYBIND11_MODULE(protocol_name, m) so I only have only one PYBIND11_MODULE() call. Here's a minimal example to describe the method better:

message1_bind.cpp:

#include <pybind11/pybind11.h>
#include "messages/message_1.h"

void init_message1(pybind11::module& m)
{
    pybind11::class_<protocol_name::Message1>(m, "Message1").def(pybind11::init<>());
    m.def("serialize_message1", &protocol_name::serialize_message_1);
    m.def("deserialize_message1", &protocol_name::deserialize_message_1);
}

And then inside main_bind.cpp

#include <pybind11/pybind11.h>
#include "message1_bind.cpp"
/// ... all other includes

PYBIND11_MODULE(protocol_name, m)
{
    init_message1(m);
    /// init_message2(m) and so on..
}

Botje · Accepted Answer · 2025-02-25 07:54:02Z

1

Why not solve this on the Python side? Assume you have message types hello and bye that are turned into org.sigsev.proto.hello.HelloMessage and org.sigsev.proto.bye.ByeMessage, respectively.

Then you can define a __init__.py in org/sigsegv/proto with the following contents:

from .hello import HelloMessage
from .bye import ByeMessage

Now the org.sigsegv.proto module will export HelloMessage and ByeMessage.

answered Feb 25 at 7:54

Botje

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1 Comment

no more sigsegv Feb 25 at 8:31

Hey, thanks for your help. I've posted the solution as an answer.

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