title: How should a python type hint require that a value has a given attribute?
body: <p>Let's say I have a simple function like this:</p>
  
  <pre class="lang-py prettyprint-override"><code>def foo(a: Any):
      return a.bar + a.baz
  </code></pre>
  
  <p>I would like to change the type hint from <code>Any</code> to one that requires (well, suggests, given that it is a type <em>hint</em>) that <code>a</code> provides the <code>bar</code> and <code>baz</code> attributes.  What should it be changed to?</p>