code: def get_app(self, reference_app=None):
          
  
          if reference_app is not None:
              return reference_app
  
          if self.app is not None:
              return self.app
  
          ctx = stack.top
  
          if ctx is not None:
              return ctx.app
  
          raise RuntimeError('Application not registered on Bouncer'
                             ' instance and no application bound'
                             ' to current context')
docs: Helper method that implements the logic to look up an application.