title: Please explain '%' usage in python
body: <p>I'm learning multithreading in python and I was reading through <a href="https://stackoverflow.com/a/13973531/8859876">this answer</a>. I understand most of the code however there is this one line which I simply don't understand and I don't know how to search for it on Google as the '%' sign keeps returning modulo.</p>
  
  <pre><code>req.headers['Range'] = 'bytes=%s-%s' % (start, start+chunk_size)
  </code></pre>
  
  <p>I thought that req.headers['Range'] would retrieve some 'range' element from an array however here they are assigning it a value of 'bytes=%s-%s' % (start, start+chunk_size). I really just don't understand what is going on in this line. Things like 'bytes=%s-%s' I am assuming is some sort of python syntax which I am unaware of. If you could explain each term in this line that would be very much appreciated.</p>