Question

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

I have to make a python function as callback of a c++ function.How to do?Where can I find some examples??
I want to use boost.python.

Answer 1

My approach to this (not the only way)

In C++ I have a class that provides a callback in the following way:

struct Mesh {
 template<class Visitor>
  void visitChildren(Visitor& v)
  {
     [...]
     v.visit([...])
  }
}

and then when I export the class to python (still C++)

struct ChildrenVisitor 
{
   ChildrenVisitor(PyObject* self)
        : self(self) 
   {}

  void visit( /* .... */ )
  {
    call_method<void>(self, "visit" /*, [...] */ );
  }

 private:
    PyObject* self; // 1
};

The export of the visitor itself to python

typedef ChildrenVisitor ClassT;
class_<ClassT, boost::noncopyable >("ChildrenVisitor",
    init<PyObject*>() );

And for the export of Mesh you do

.def("visitChildren", &Mesh::template visitChildren<ChildrenVisitor> )

I always used ... where you can insert any of your arguments.

In python you do something like this

class MyVisitor(ChildrenVisitor): 
  def __init__(self):
    ChildrenVisitor.__init__(self,self)

  def visit(self):
    # do whatever you want

I also like to make a subclass of ChildrenVisitor that accepts lambda functions, that makes writing visitors in python single lines.

---

Oh, btw. if you want to call the function at some later point then you would need to change the C++ implementation to something like this

struct ChildrenVisitorBase 
{
  virtual void visit( /* .... */ ) = 0;
};

struct Mesh {
  void registerCallback(shared_ptr<ChildrenVisitorBase> v)
  {
     visitors.push_back(v)
  }

  void doSomeWork() {
    // ...
    for(int i=0; i < visitors.size(); ++i)
      visitors[i]->visit( /* ... */ )
  }

  std::vector<  shared_ptr<ChildrenVisitorBase> > visitors;
}

And make ChildrenVisitor implement ChildrenVisitorBase.