code: def exportable_keys(self):
      
      keys = collections.defaultdict(list)
      for tup in self._tuples:
        for key, private in tup._keys_and_privacy().items():
          keys[key].append(private)
      return [k for k, ps in keys.items() if not any(ps)]
docs: Return a list of keys that are exportable from this tuple.
  
      Returns all keys that are not private in any of the tuples.