There is currently a pickling bug in the namedtuple factory:

  >>> from collections import namedtuple
  >>> MemoRecord = namedtuple("MemoRecord", "key, msg")
  >>> m = MemoRecord(1,"hello")
  >>> import pickle
  >>> pickle.loads(pickle.dumps(m))
  Traceback (most recent call last):
    ...
  TypeError: __new__() takes exactly 3 positional arguments (2 given)

The bug is due to the fact that classes created by namedtuple don't
handle the __new__ arguments in the same fashion as tuple.__new__. The
fix is simply to define __getnewargs__.