# How Julia call Pybind11 code?

**URL:** <https://discourse.julialang.org/t/how-julia-call-pybind11-code/40787>\
**Category:** General Usage\
**Tags:** question\
**Created:** [June 5, 2020, 2:49am UTC](https://discourse.julialang.org/t/how-julia-call-pybind11-code/40787 "2020-06-05T02:49:27Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![agdkyang](https://avatars.discourse-cdn.com/v4/letter/a/ecc23a/32.png) [@agdkyang](https://discourse.julialang.org/u/agdkyang)\
**Post date:** [June 5, 2020, 2:49am UTC](https://discourse.julialang.org/t/how-julia-call-pybind11-code/40787/1 "2020-06-05T02:49:27Z")

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Pybind11 code :

#include \<pybind11/embed.h\>  
#include   
namespace py = pybind11;  
extern “C”{  
int init() {  
py::scoped\_interpreter python;  
auto math = py::module::import(“math”);  
double root\_two = math.attr(“sqrt”)(2.0).cast();  
std::cout \<\< "The square root of 2 is: " \<\< root\_two \<\< “\n”;  
} }

I will generate a dynamic library libtest.so by using the above code and link to libpython3.7m.so. However, when Julia uses “ccall” method to call libtest.so, math.cpython-37m-x86\_64-linux-gnu.so cannot link to libpython3.7m.so and generates error like this undefined symbol: PyArg\_Parse. But when c language call libtest.so ,there is no problem. I don’t know why math.cpython-37m-x86\_64-linux-gnu.so cannot link to libpython3.7m.so directly when using julia language. And how to solve this problem?

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**Author:** ![yuyichao](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/yuyichao/32/20_2.png) [@yuyichao](https://discourse.julialang.org/u/yuyichao)\
**Post date:** [June 5, 2020, 3:51am UTC](https://discourse.julialang.org/t/how-julia-call-pybind11-code/40787/2 "2020-06-05T03:51:15Z")

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As I said in the github issue, please quote your code.

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I believe the issue is in general python modules don’t link libpython presumably to avoid pulling in a different one than the one loading the module with the assumption that the loading process already has libpython loaded.

But IIRC on linux julia use RTLD\_LOCAL by default, meaning the symbol from libpython aren’t in the global scope and the module can’t find it. The solution is that you have to directly or indirectly `dlopen` `libpython` with `RTLD_GLOBAL`. If your library is linked to python, dlopening your library should be enough.

* * *

As an aside, I think linux has a extension that allow application to load libraries into it’s own namespace. If python uses that this probably won’t be an issue anymore… (edit: hmmm, actually that seems to be the default behavior and RTLD\_LOCAL does not seem to be the same as a new namespace…)