code: def _register_signal_handler(self, description, signal, handler):
          
          from flask import signals
  
          if not signals.signals_available:
              self.app.logger.warn('blinker needs to be installed in order to support %s'.format(description))
          self.app.logger.info('Enabling {}'.format(description))
          # Weak references won't work if handlers are methods rather than functions.
          signal.connect(handler, sender=self.app, weak=False)
docs: Registers a handler for the given signal.
          :param description: a short description of the signal to handle.
          :param signal: the signal to handle.
          :param handler: the function to use for handling the signal.