How to use the forbiddenfruit.__init__.PyTypeObject._fields_ function in forbiddenfruit

setattr(tyobj, tp_as_name, tp_as_new_ptr)
        tp_as = tp_as_ptr[0]

        # find the C function type
        for fname, ftype in struct_ty._fields_:
            if fname == impl_method:
                cfunc_t = ftype

        cfunc = cfunc_t(wrapper)
        tp_func_dict[(klass, attr)] = cfunc

        setattr(tp_as, impl_method, cfunc)
    else:
        # find the C function type
        for fname, ftype in PyTypeObject._fields_:
            if fname == impl_method:
                cfunc_t = ftype

        if not (klass, attr) in tp_as_dict:
            tp_as_dict[(klass, attr)] = ctypes.cast(getattr(tyobj, impl_method), cfunc_t)

        # override function call
        cfunc = cfunc_t(wrapper)
        tp_func_dict[(klass, attr)] = cfunc
        setattr(tyobj, impl_method, cfunc)

class PyMappingMethods(ctypes.Structure):
    pass

class PyTypeObject(ctypes.Structure):
    pass

class PyAsyncMethods(ctypes.Structure):
    pass


PyObject._fields_ = [
    ('ob_refcnt', Py_ssize_t),
    ('ob_type', ctypes.POINTER(PyTypeObject)),
]

PyTypeObject._fields_ = [
    # varhead
    ('ob_base', PyObject),
    ('ob_size', Py_ssize_t),
    # declaration
    ('tp_name', ctypes.c_char_p),
    ('tp_basicsize', Py_ssize_t),
    ('tp_itemsize', Py_ssize_t),
    ('tp_dealloc', ctypes.CFUNCTYPE(None, PyObject_p)),
    ('printfunc', ctypes.CFUNCTYPE(ctypes.c_int, PyObject_p, FILE_p, ctypes.c_int)),
    ('getattrfunc', ctypes.CFUNCTYPE(PyObject_p, PyObject_p, ctypes.c_char_p)),
    ('setattrfunc', ctypes.CFUNCTYPE(ctypes.c_int, PyObject_p, ctypes.c_char_p, PyObject_p)),
    ('tp_as_async', ctypes.CFUNCTYPE(PyAsyncMethods)),
    ('tp_repr', ctypes.CFUNCTYPE(PyObject_p, PyObject_p)),
    ('tp_as_number', ctypes.POINTER(PyNumberMethods)),
    ('tp_as_sequence', ctypes.POINTER(PySequenceMethods)),
    ('tp_as_mapping', ctypes.POINTER(PyMappingMethods)),