title: Convert "unknown format" strings to datetime objects?
body: <p>This is probably a very basic question but after reading documentation I still can't figure out how to do it...</p>
  
  <p>I have two strings in Python that contain dates of <em>unknown format</em>. I don't know what formats they are in, except I know that both are valid date-time expressions. For example, one of them might be in the ISO format and the other in some other format.</p>
  
  <p>All I need is to be able to compare the dates. What's the correct way to turn strings into appropriate date-time objects so that they can be compared?</p>
  
  <p>thanks!</p>