code: def default_datastore_policy(key):
      
      flag = None
      if key is not None:
        modelclass = model.Model._kind_map.get(key.kind())
        if modelclass is not None:
          policy = getattr(modelclass, '_use_datastore', None)
          if policy is not None:
            if isinstance(policy, bool):
              flag = policy
            else:
              flag = policy(key)
      return flag
docs: Default datastore policy.
  
      This defers to _use_datastore on the Model class.
  
      Args:
        key: Key instance.
  
      Returns:
        A bool or None.