code: def default(cls):
          
          with enamlnative.imports():
              for impl in [
                  TornadoEventLoop,
                  TwistedEventLoop,
                  BuiltinEventLoop,
              ]:
                  if impl.available():
                      print("Using {} event loop!".format(impl))
                      return impl()
          raise RuntimeError("No event loop implementation is available. "
                             "Install tornado or twisted.")
docs: Get the first available event loop implementation
          based on which packages are installed.