How to pass ROOT objects from a C++ library to Python?

[Serguei_Kolos1]

Hello

Could someone advice me please or point to a documentation explaining how to pass a histogram that has been created and filled in a C++ library to a Python script. Here is what I’m doing in the library:

    TH1* get_h() {
        TH1 * h = new TH1I("test", "test", 1000, 0, 50000);
        ...
        return h;
    }

   BOOST_PYTHON_MODULE(libfast_plugin_py)
   {
     boost::python::def("get_h", &get_h, return_value_policy<manage_new_object>());
   }

And here is the Python script:

import ROOT
from libfast_plugin_py import get_h
h = get_h()

which throws the following error:

    h = get_h()
        ^^^^^^^
TypeError: No Python class registered for C++ class TH1

[mczurylo]

Hi @Serguei_Kolos1,

to include C++ libraries in ROOT you can read this page of our manual: Python interface: PyROOT - ROOT and use ROOT.gInterpreter.Declare to define your C++ function.

Cheers,
Marta