code: def configure(
          cls, impl: "Union[None, str, Type[Configurable]]", **kwargs: Any
      ) -> None:
          
          super(AsyncHTTPClient, cls).configure(impl, **kwargs)
docs: Configures the `AsyncHTTPClient` subclass to use.
  
          ``AsyncHTTPClient()`` actually creates an instance of a subclass.
          This method may be called with either a class object or the
          fully-qualified name of such a class (or ``None`` to use the default,
          ``SimpleAsyncHTTPClient``)
  
          If additional keyword arguments are given, they will be passed
          to the constructor of each subclass instance created.  The
          keyword argument ``max_clients`` determines the maximum number
          of simultaneous `~AsyncHTTPClient.fetch()` operations that can
          execute in parallel on each `.IOLoop`.  Additional arguments
          may be supported depending on the implementation class in use.
  
          Example::
  
             AsyncHTTPClient.configure("tornado.curl_httpclient.CurlAsyncHTTPClient")