title: Correct way to detect sequence parameter?
body: <p>I want to write a function that accepts a parameter which can be either a sequence or a single value. The type of value is str, int, etc., but I <strong>don't</strong> want it to be restricted to a hardcoded list. 
  In other words, I want to know if the parameter X is a sequence or something I have to convert to a sequence to avoid special-casing later. I could do</p>
  
  <p><code>type(X) in (list, tuple)</code></p>
  
  <p>but there may be other sequence types I'm not aware of, and no common base class.</p>
  
  <p>-N.</p>
  
  <p><strong>Edit</strong>: See my "answer" below for why most of these answers don't help me. Maybe you have something better to suggest.</p>