Base class can access derived member function ??

[faalbers]

I have a binding cpp as follow:

#include <pybind11/pybind11.h>
#include <iostream>

namespace py = pybind11;

class Pet
{
public:
    Pet(const std::string &name) : name(name) { }

    //virtual void blah() {}

    std::string name;
};

class Dog : public Pet
{
public:
    Dog(const std::string &name) : Pet(name) { }

    void bark() { std::cout << "Woof!\n"; }
};

PYBIND11_MODULE(pcourse, m)
{
    m.doc() = "pybind11 Course with examples";

    // binding a class
    py::class_<Pet>(m, "Pet")
        .def(py::init<const std::string &>())
        .def_readwrite("name", &Pet::name)
        ;
    
    // Inheritance template parameter
    py::class_<Dog, Pet>(m, "Dog")
        .def(py::init<const std::string &>())
        .def("bark", &Dog::bark)
        ;
    
    // Return a base pointer to a derived instance
    m.def("pet_store", []() { return std::unique_ptr<Pet>(new Dog("Bijou")); });
}

When I run the Python code:

import pcourse as example

pet = example.pet_store()
print(pet)
print(type(pet))
pet.bark()

as expected, I get a "AttributeError: 'pcourse.Pet' object has no attribute 'bark'" error

But when I uncomment "virtual void blah() {}" and build the module, I get no error and it prints "Woof!"

It should not do that because it is a base class. Anyone know why ?

Thanks

[faalbers]

Never mind !! The manual explains why ! Duh !!!

The function returned a Dog instance, but because it’s a non-polymorphic type behind a base pointer,
Python only sees a Pet. In C++, a type is only considered polymorphic if it has at least one virtual function
and pybind11 will automatically recognize this: