Protected methods are skipped.

[yak]

Consider this pure virtual class:

class Foo
{
public:
    virtual void Bar()=0;
protected:
    void Baz();
}

Currently pybindgen skips the Baz method, even while providing the helper class (when allow_subclassing=True). A Python subclass can provide an implementation for Bar but it won't be able to call Baz.

A viable solution would be to add a public trampoline method to the helper class. The method would ball Baz and it would be wrapped and made available to Python under the name Baz. Of course in such case it would be callable from anywhere but that's fine, it's like Python works after all.