In a sense, *all* objects are instances of new-style classes in 2.x, including instances of old-style classes (which are instances of the InstanceType type, which is a type, and hence a new-style class).

You may want to look at the __flags__ property of the type object. If it is a heap type, there is a good chance that it was created through a class statement. Alternatively, you can look at the type's __module__, and find out whether the module is a Python module.