code: def _register_jobs(self):
          
  
          # job_name is hard-corded
          job_name = 'ConcreteJob'
          modules = self._get_modules()
  
          for section, options in self.config.items():
  
              if section == 'global':
                  continue
  
              try:
                  name = options['module']
              except KeyError:
                  raise ConfigMissingValue(section, 'module')
  
              try:
                  job = getattr(modules[name], job_name)
                  self.notify(name, job)
              except KeyError:
                  raise NotSupportedError(name)
docs: This method extracts only the "ConcreteJob" class
          from modules that were collected by ConfigReader._get_modules().
          And, this method called Subject.notify(),
          append "ConcreteJob" classes to JobObserver.jobs.