title: Python 3 type hint for string options
body: <p>Let's say, I have a function with a string argument corresponding for a method name:</p>
  
  <pre><code>def func(method: str):
      if method not in ('simple_method', 'some_other_method'):
          raise ValueError('Unknown method')
  </code></pre>
  
  <p>Can I add all the possible supported options (strings) as a type hint for this argument? For instance, something like this (which doesn't work since there is no Str in typing):</p>
  
  <pre><code>from typing import Str
  
  def func(method: Str['simple_method', 'some_other_method']):
      ...
  </code></pre>