title: Type hints: solve circular dependency
body: <p>The following produces <code>NameError: name 'Client' is not defined</code>. How can I solve it?</p>
  
  <pre><code>class Server():
      def register_client(self, client: Client)
          pass
  
  
  class Client():
      def __init__(self, server: Server):
          server.register_client(self)
  </code></pre>