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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 RegisterDecoder(cls, decoder):
 """Registers a decoder for a specific encoding method. Args: decoder (type):
 decoder class. Raises: KeyError: if the corresponding decoder is already set. """

    encoding_method = decoder.ENCODING_METHOD.lower()
    if encoding_method in cls._decoders:
      raise KeyError(
          'Decoder for encoding method: {0:s} already set.'.format(
              decoder.ENCODING_METHOD))

    cls._decoders[encoding_method] = decoder