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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _get_input_readers(self, state):
 """Get input readers. Args: state: a MapreduceState model. Returns: A tuple: (a list of input readers, a model._HugeTaskPayload entity). The payload entity contains the json serialized input readers. (None, None) when input reader inplitting returned no data to process. """

    serialized_input_readers_key = (self._SERIALIZED_INPUT_READERS_KEY %
                                    state.key().id_or_name())
    serialized_input_readers = model._HugeTaskPayload.get_by_key_name(
        serialized_input_readers_key, parent=state)

    # Initialize input readers.
    input_reader_class = state.mapreduce_spec.mapper.input_reader_class()
    split_param = state.mapreduce_spec.mapper
    if issubclass(input_reader_class, map_job.InputReader):
      split_param = map_job.JobConfig._to_map_job_config(
          state.mapreduce_spec,
          os.environ.get("HTTP_X_APPENGINE_QUEUENAME"))
    if serialized_input_readers is None:
      readers = input_reader_class.split_input(split_param)
    else:
      readers = [input_reader_class.from_json_str(_json) for _json in
                 json.loads(zlib.decompress(
                 serialized_input_readers.payload))]

    if not readers:
      return None, None

    # Update state and spec with actual shard count.
    state.mapreduce_spec.mapper.shard_count = len(readers)
    state.active_shards = len(readers)

    # Prepare to save serialized input readers.
    if serialized_input_readers is None:
      # Use mr_state as parent so it can be easily cleaned up later.
      serialized_input_readers = model._HugeTaskPayload(
          key_name=serialized_input_readers_key, parent=state)
      readers_json_str = [i.to_json_str() for i in readers]
      serialized_input_readers.payload = zlib.compress(json.dumps(
                                                       readers_json_str))
    return readers, serialized_input_readers