How can I pickle a dynamically created nested class in python?

Question

I have a nested class:

class WidgetType(object):
    
    class FloatType(object):
        pass
    
    class TextType(object):
        pass

.. and

Answer 1

In Sage (www.sagemath.org), we have many instances of this pickling issue. The way we decided to systematically solve it is to put the outer class inside a specific metaclass whose goal is to implement and hide the hack. Note that this automatically propagate through nested classes if there are several level of nesting.