title: Python: get datetime for '3 years ago today'
body: <p>In Python, how do I get a datetime object for '3 years ago today'?</p>
  
  <p>UPDATE: FWIW, I don't care hugely about accuracy... i.e. it's Feb 29th today, I don't care whether I'm given Feb 28th or March 1st in my answer. Concision is more important than configurability, in this case.</p>