VectorLen retrieves the length of the vector whose offset is stored
           at "off" in this object.

def VectorLen(self, off):
        """VectorLen retrieves the length of the vector whose offset is stored
           at "off" in this object."""
        N.enforce_number(off, N.UOffsetTFlags)

        off += self.Pos
        off += encode.Get(N.UOffsetTFlags.packer_type, self.Bytes, off)
        ret = encode.Get(N.UOffsetTFlags.packer_type, self.Bytes, off)
        return ret