code: def getPreprocessor(self, service_request):
          
          preproc = service_request.service.getPreprocessor(service_request)
  
          if preproc is None:
              return self.preprocessor
  
          return preproc
docs: Gets a preprocessor callable based on the service_request. This is
          granular, looking at the service method first, then at the service
          level and finally to see if there is a global preprocessor function
          for the gateway. Returns C{None} if one could not be found.