'Provides information about all fragments that were found in the object
directory, including fragments without a matching durable file, and
including any fragment chosen to construct the opened diskfile.
:return: A dict mapping <Timestamp instance> -> <list of frag indexes>,
or None if the diskfile has not been opened or no fragments
were found.'

@property
def fragments(self):

    if self._ondisk_info:
        frag_sets = self._ondisk_info['frag_sets']
        return dict([(ts, [info['frag_index'] for info in frag_set]) for (ts, frag_set) in frag_sets.items()])
