title: Boto3: grabbing only selected objects from the S3 resource
body: <p>I can grab and read all the objects in my AWS S3 bucket via </p>
  
  <pre><code>s3 = boto3.resource('s3')
      bucket = s3.Bucket('my-bucket')
      all_objs = bucket.objects.all()
      for obj in all_objs:
          pass
          #filter only the objects I need
  </code></pre>
  
  <p>and then</p>
  
  <pre><code>obj.key
  </code></pre>
  
  <p>would give me the path within the bucket.</p>
  
  <p>Is there a way to filter beforehand for only those files respecting a certain starting path (a directory in the bucket) so that I'd avoid looping over all the objects and filtering later?</p>