>>> import boto
>>> c = boto.connect_s3()
>>> bucket = c.lookup('mybucketname')
>>> l = [(k.last_modified, k) for k in bucket]
>>> key_to_download = sorted(l, cmp=lambda x,y: cmp(x[0], y[0]))[-1][1]
>>> key_to_download.get_contents_to_filename('myfile')

>>> import boto
>>> c = boto.connect_s3()
>>> bucket = c.get_bucket('mybucketname')
>>> bucket_files = bucket.list('subdir/file_2014_')
>>> l = [(k.last_modified, k) for k in bucket_files]
>>> key_to_download = sorted(l, cmp=lambda x,y: cmp(x[0], y[0]))[-1][1]
>>> key_to_download.get_contents_to_filename('target_filename')