code: def bind(self, flask_app, service, group=None):
          
          if group not in self.services[service]:
              raise RuntimeError(
                  'API group {} does not exist in service {}'.format(
                      group, service)
              )
          for name, api in self.services[service][group].items():
              # only bind APIs that have views associated with them
              if api.view_fn is None:
                  continue
              if name not in flask_app.view_functions:
                  flask_app.add_url_rule(
                      api.url, name, view_func=api.view_fn, **api.options)
docs: Bind the service API urls to a flask app.