title: File extension naming: .p vs .pkl vs .pickle
body: <p>When reading and writing pickle files, I've noticed that some snippets use <code>.p</code> others <code>.pkl</code> and some the full <code>.pickle</code>.  Is there one most pythonic way of doing this?</p>
  
  <p>My current view is that there is no one right answer, and that any of these will suffice.  In fact, writing a filename of <code>awesome.pkl</code> or <code>awesome.sauce</code> won't make a difference when running <code>pickle.load(open(filename, "rb"))</code>.  This is to say, the file extension is just a convention which doesn't actually affect the underlying data.  Is that right?</p>
  
  <p>Bonus: What if I saved a PNG image as <code>myimage.jpg</code>?  What havoc would that create?</p>