code: def get_last_version(self, filename):
          
          def ok(doc):
              if doc is None:
                  raise NoFile("TxMongo: no file in gridfs with filename {0}".format(repr(filename)))
  
              return GridOut(self.__collection, doc)
  
          return self.__files.find_one({"filename": filename},
                                       filter = filter.sort(DESCENDING("uploadDate"))).addCallback(ok)
docs: Get a file from GridFS by ``"filename"``.
  
          Returns the most recently uploaded file in GridFS with the
          name `filename` as an instance of
          :class:`~gridfs.grid_file.GridOut`. Raises
          :class:`~gridfs.errors.NoFile` if no such file exists.
  
          An index on ``{filename: 1, uploadDate: -1}`` will
          automatically be created when this method is called the first
          time.
  
          :Parameters:
            - `filename`: ``"filename"`` of the file to get
  
          .. versionadded:: 1.6