title: Pymongo error : 'Cursor' object has no attribute 'find' , how to filter it?
body: <p>I want to query data from mongo and filter them to many stacks<br>
  The logic is like: </p>
  
  <pre><code>objs = collection.find({"name":"BOB"})
  
  t_list = ["Math","History"]
  
  for t in t_list : 
      subjects = objs.find({{"subjects":t}}) 
      # do_somethig(subjects)
  </code></pre>
  
  <p>But pymongo will raise error  <code>AttributeError: 'Cursor' object has no attribute 'find'</code>  </p>
  
  <p>I want to know can pymongo do this ?? ( query one time and then filter the data I want??) </p>