title: List AWS S3 folders with boto3
body: <p>I have boto code that collects S3 sub-folders in levelOne folder:</p>
  
  <pre><code>import boto
  
  s3 = boto.connect_s3()
  bucket = s3.get_bucket("MyBucket")
  
  for level2 in bucket.list(prefix="levelOne/", delimiter="/"):
      print(level2.name)
  </code></pre>
  
  <p>Please help to discover similar functionality in boto3. The code should not iterate through all S3 objects because the bucket has a very big number of objects.</p>