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Solve the following problem using Python, implementing the functions described below, one line at a time
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<USER_TASK:>
Description:
 def decode_payload(cls, request):
 """Decode task payload. HugeTask controls its own payload entirely including urlencoding. It doesn't depend on any particular web framework. Args: request: a webapp Request instance. Returns: A dict of str to str. The same as the params argument to __init__. Raises: DeprecationWarning: When task payload constructed from an older incompatible version of mapreduce. """

    # TODO(user): Pass mr_id into headers. Otherwise when payload decoding
    # failed, we can't abort a mr.
    if request.headers.get(cls.PAYLOAD_VERSION_HEADER) != cls.PAYLOAD_VERSION:
      raise DeprecationWarning(
          "Task is generated by an older incompatible version of mapreduce. "
          "Please kill this job manually")
    return cls._decode_payload(request.body)