code: def incrby(self, fmt, offset, increment, overflow=None):
          
          bfo = BitFieldOperation(self.database, self.key)
          return bfo.incrby(fmt, offset, increment, overflow)
docs: Increment a bitfield by a given amount.
  
          :param fmt: format-string for the bitfield being updated, e.g. u8 for
              an unsigned 8-bit integer.
          :param int offset: offset (in number of bits).
          :param int increment: value to increment the bitfield by.
          :param str overflow: overflow algorithm. Defaults to WRAP, but other
              acceptable values are SAT and FAIL. See the Redis docs for
              descriptions of these algorithms.
          :returns: a :py:class:`BitFieldOperation` instance.