pass callback from python to c++ using boost::python

Question

I want to pass callback from my python code to c++

I want my code look something like this: In C++ :

typedef void (*MyCallback_t) (CallbackInfo);

class MyClass
{...
   void setcallback(MyCallback_t cb);
 ...
}

And to use it in python :

import mylib

def myCallback(mylib_CallbackInfo):
...

t = mylib.MyClass()
t.setcallback(myCallback)

I saw some topics near my problem but couldn't solve it

For example here : Realtime processing and callbacks with Python and C++ there is advice to use boost::python and warning about GLI but no examples. And here

How to call a python function from a foreign language thread (C++) there is no full description with python code part and with "BOOST_PYTHON_MODULE" part

I also found link to use py_boost_function.hpp for example in Boost python howto but it didn't compile and actualy I couldn't understand how to use it.

+1 Great question. Just what I was looking for!

Alba Mendez
– Alba Mendez

2011-11-20 10:53:07 +00:00
Commented Nov 20, 2011 at 10:53 — Alba Mendez
– Alba Mendez, Commented Nov 20, 2011 at 10:53

nont · Accepted Answer · 2014-07-09 15:09:01Z

22

Ok, I'm still trying to figure this out too, but here's whats working for me so far:

#this is the variable that will hold a reference to the python function
PyObject *py_callback;

#the following function will invoked from python to populate the call back reference
PyObject *set_py_callback(PyObject *callable)
{
    py_callback = callable;       /* Remember new callback */
    return Py_None;
}
...
#Initialize and acquire the global interpreter lock
PyEval_InitThreads();

#Ensure that the current thread is ready to call the Python C API 
PyGILState_STATE state = PyGILState_Ensure();

#invoke the python function
boost::python::call<void>(py_callback);

#release the global interpreter lock so other threads can resume execution
PyGILState_Release(state);

The python function is invoked from C++, and executes as expected.

edited Jul 9, 2014 at 15:09

answered Sep 30, 2011 at 2:53

nont

9,5597 gold badges65 silver badges83 bronze badges

Sign up to request clarification or add additional context in comments.

8 Comments

Igor Pavlov Over a year ago

Yes, I did it exactly like you. But forgot to write here about it.

Sven Over a year ago

Is there a lack of reference counting in this example?

Pat Mustard Over a year ago

How would you pass data such as a vector<int> to the python callback?

thomas Over a year ago

I'm very interested in this question. Would you care to elaborate on this answer? Could you explain what each line of code is doing?

nont Over a year ago

Sure! its been awhile since I did this, but I've annotated each line for you. googling for each function will find you more documentation.

|

duxtinto · Accepted Answer · 2020-11-19 18:55:18Z

3

These test files from the boost::python source code repository contains great examples about how to pass callbacks from Python into C++:

answered Nov 19, 2020 at 18:55

duxtinto

5196 silver badges6 bronze badges

1 Comment

Sabito Over a year ago

A link to a solution is welcome, but please ensure your answer is useful without it: add context around the link so your fellow users will have some idea what it is and why it’s there, then quote the most relevant part of the page you're linking to in case the target page is unavailable. Answers that are little more than a link may be deleted.

Collectives™ on Stack Overflow

pass callback from python to c++ using boost::python

2 Answers 2

8 Comments

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

8 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related