title: Do something every time a list length increases by a certain amount
body: <p>I want my code to take a break every time one of my list (tumblr or save) reaches 300 entries (ie: 300, 600, 900, etc.)</p>
  
  <p>This is my code:</p>
  
  <pre><code>tumblr = []
  for half_hour in range(start_ts, until_ts, (60*30)):
      save = []
      try:
          data = client.tagged("fanart", before=half_hour)
              save.append(list([row[4], row[8], row[0], title, desc, url, row[5]]))
              print(row[8], title)
          if (len(tumblr) % 300 == 0) or (len(save) % 300 == 0):
              sauvegarde()
              time.sleep(60)
  </code></pre>
  
  <p>I didn't put the whole script but tumblr gets filled later on in the script so at first the list has zero entry.</p>
  
  <p>The problem I seem to have is that it starts right away with zero. Is there a way to disregard zero in this logic ?</p>
  
  <p>Thanks</p>