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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 _GetRequestClass(self, method_descriptor):
 """Returns the class of the request protocol message. Args: method_descriptor: Descriptor of the method for which to return the request protocol message class. Returns: A class that represents the input protocol message of the specified method. """

    if method_descriptor.containing_service != self.descriptor:
      raise RuntimeError(
          'GetRequestClass() given method descriptor for wrong service type.')
    return method_descriptor.input_type._concrete_class