title: What are an 'object's attributes' in python and in general?
body: <p>I'm learning python and one of the built-in functions being taught is <code>dir()</code> -- the course describes it as <em>'returning the directory of valid attributes for an object,'</em> but what are an object's attributes? </p>
  
  <p>I think I see some member functions in the returned list of attributes, <code>__len__</code> I assume refers to <code>len()</code>, but what are all these other things listed?</p>
  
  <p><img src="https://i.stack.imgur.com/bWqCx.png" alt="Course description"></p>
  
  <p>Also, what does it mean, it can be incomplete?</p>
  
  <p>This is my first question and I wouldn't ask it if I didn't already spend 45 minutes trying to figure this out. </p>