undefined reference to `PyCMethod_New'

[EnziinSystem]

My environment:

Ubuntu 20.04
Python 3.8.10

When I run compile a program use pybind11, it raise a error:

/usr/bin/ld: ../scripting/libscripting.a(python_scripting.cpp.o): in function `pybind11::cpp_function::initialize_generic(std::unique_ptr<pybind11::detail::function_record, pybind11::cpp_function::InitializingFunctionRecordDeleter>&&, char const*, std::type_info const* const*, unsigned long)':
/home/../ubuntu/kicad/thirdparty/pybind11/include/pybind11/pybind11.h:415: undefined reference to `PyCMethod_New'
collect2: error: ld returned 1 exit status
make[2]: *** [bitmap2component/CMakeFiles/bitmap2component.dir/build.make:191: bitmap2component/bitmap2component] Error 1
make[1]: *** [CMakeFiles/Makefile2:3754: bitmap2component/CMakeFiles/bitmap2component.dir/all] Error 2
make[1]: *** Waiting for unfinished jobs....

[jiwaszki]

Without minimal example it is hard to tell, but I think that linking is source of your problem.

Look at these two stacks:

• https://stackoverflow.com/a/61085569
• https://stackoverflow.com/questions/27672572/embedding-python-in-c-linking-fails-with-undefined-reference-to-py-initialize

[Keepmoving-ZXY]

The same problem in my project, and I am working on a simple cast to reproduct this error.

[G-Pereira]

What was the issue @Keepmoving-ZXY ? I need to fix it in mine as well

[Keepmoving-ZXY]

According to my memory, I solve this problem by changing another version of python.

[G-Pereira]

That and updating from Ubuntu 20.04 to 22.04, and updating pyside fixed it for me as well. Here was my changes (I did not test which was the culprit):

opulo-inc/lumenpnp@7d21ffd

[NumbNutN]

Hi, I've solve the problem by update my Python interpreter version to 3.9.18. There's definitely no symbol definition for PyCMethod_New in libpython3.8.so. But I can find it in libpython3.9.so

$ readelf -s lib/libpython3.9.so | grep "PyCMethod"
   489: 0000000000121070   460 FUNC    GLOBAL DEFAULT   11 PyCMethod_New
  1921: 0000000000365ac0   408 OBJECT  GLOBAL DEFAULT   21 PyCMethod_Type
   443: 00000000000696d4   103 FUNC    LOCAL  DEFAULT   11 PyCMethod_New.cold
 36122: 0000000000121070   460 FUNC    GLOBAL DEFAULT   11 PyCMethod_New
 37245: 0000000000365ac0   408 OBJECT  GLOBAL DEFAULT   21 PyCMethod_Type

Notice PyCMethod_New is part of the stable ABI in Python Standard Library since version 3.9.
Python Doc - PyCMethod_New

[roastduck]

PyCMethod_New was added in Python 3.9 (https://docs.python.org/3/c-api/structures.html#c.PyCMethod_New), so it is definately not found in Python 3.8. Does that mean pybind11 requires Python >= 3.9?

In my case, the problem turned out to be that I used the Python_FIND_STRATEGY=VERSION mode of FindPython in CMake. In this mode. This is the default mode of my CMake version.

In this mode, CMake will try to find the latest version of Python, even if it is not the first Python in your path. In this case, you will end up including headers from a newer Python whiling executing an older Python, and the older Python cannot link against symbols from the newer header. Setting Python_FIND_STRATEGY=LOCATION solves the problem.