title: Python finding minimum values of functions of list items, but returning the list item
body: <p>Sorry, it's a bit hard to explain my question in a title, but basically, I have a list of positions, and each position can be passed through a function to get a number that gives you data about the position. What I want to do is return the position with the lowest data value in the list, but I can't seem to find a way to do this.</p>
  
  <p>A bit of pseudo code should help:</p>
  
  <pre><code>def posfunc(self,pos):
      x,y = pos
      return x**2-y
  
  def minpos(self)
      returns position with the least x**2-y value
  </code></pre>