title: Pymongo multi update query
body: <p>I have the following query</p>
  
  <pre><code>DB_HOST = '127.0.0.1'
  COLLECTION = 'scraper'
  db = pymongo.MongoClient(DB_HOST)[COLLECTION]['scrap']
  db.update({'indice':0, 'thread_id':{'$in':list_to_update}},{'updated':'yes'}, multi=True)
  </code></pre>
  
  <p>where list_to_update is a list of thread_ids where I would like to insert the field 'updated' to 'yes'</p>
  
  <p>I am receiving the following error</p>
  
  <pre><code>pymongo.errors.OperationFailure: multi update only works with $ operators
  </code></pre>
  
  <p>Any ideas?</p>