title: Preferred (or most common) file extension for a Python pickle
body: <p>At times, I've seen <code>.pickle</code>, <code>.pck</code>, <code>.pcl</code>, and <code>.db</code> for files that contain Python pickles, but I am unsure what is the most common or best practice. I know that the latter three extensions are also used for other things.</p>
  <p>The related question is: What MIME type is preferred for sending pickles between systems using a REST API?</p>