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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 DeregisterDecrypter(cls, decrypter):
 """Deregisters a decrypter for a specific encryption method. Args: decrypter (type):
 decrypter class. Raises: KeyError: if the corresponding decrypter is not set. """

    encryption_method = decrypter.ENCRYPTION_METHOD.lower()
    if encryption_method not in cls._decrypters:
      raise KeyError(
          'Decrypter for encryption method: {0:s} not set.'.format(
              decrypter.ENCRYPTION_METHOD))

    del cls._decrypters[encryption_method]