code: def get(self, file_id):
          
          def ok(doc):
              if doc is None:
                  raise NoFile("TxMongo: no file in gridfs with _id {0}".format(repr(file_id)))
  
              return GridOut(self.__collection, doc)
          return self.__collection.files.find_one({"_id": file_id}).addCallback(ok)
docs: Get a file from GridFS by ``"_id"``.
  
          Returns an instance of :class:`~gridfs.grid_file.GridOut`,
          which provides a file-like interface for reading.
  
          :Parameters:
            - `file_id`: ``"_id"`` of the file to get
  
          .. versionadded:: 1.6