I don't think this has anything to do with namedtuple; it's true whenever you create a class in an inner scope (rather than at module level). This is by design, and these restrictions are documented: https://docs.python.org/3.6/library/pickle.html#what-can-be-pickled-and-unpickled

For example, running this script:

    import pickle

    def my_func():
        class A:
            pass

        a = A()
        return a

    a = my_func()
    pickle.dumps(a)

produces:

    Traceback (most recent call last):
      File "test.py", line 11, in <module>
        pickle.dumps(a)
    AttributeError: Can't pickle local object 'my_func.<locals>.A'