I can “pickle local objects” if I use a derived class?

Question

The pickle reference states that the set of objects which can be pickled is rather limited. Indeed, I have a function which returns a dinamically-generated clas

Answer 1

You can only pickle instances of classes defined at module's top level.

However, you can pickle instances of locally-defined classes if you promote them to top level.

You must set the __ qualname__ class attribute of the local class. Then you must assign the class to a top-level variable of the same name.

def define_class(name):
    class local_class:
        pass
    local_class.__qualname__ = name
    return local_class

class_A = define_class('class_A') # picklable
class_B = define_class('class_B') # picklable
class_X = define_class('class_Y') # unpicklable, names don't match