title: Python 3.5 type hinting dynamically generated instance attributes
body: <p>I'd like to add Python 3.5 type hints for dynamically generated object attributes, so that IDEs correctly autocomplete them. Here by "dynamical" I mean that the attribute is not present during class creation or in <code>__init__</code> or any other method.</p>
  
  <p>E.g. is there a way to add these through comments or other tricks? If not I can fallback to add dummy class attributes.</p>
  
  <p>Example::</p>
  
  <pre><code> class Request:
        """Example HTTP request object.
  
        We have `get_user()`  but we do not declare it anyhere.
        """
  
   ...
  
  
   # Pyramid's way of plugging in methods and properties to request, enabled addon capabilities for the framework
   # adds Request.user - done in different part of application lifecycle, not during class creation
   config.add_request_method(auth.get_user, 'user', reify=True)
  </code></pre>
  
  <p>The goal is to make this work so that PyCharm and other IDEs would complete this attribute.</p>