code: def read_var_uint64(self):
          
          i = self._read_varint_helper()
          if not 0 <= i <= wire_format.UINT64_MAX:
              raise errors.DecodeError('Value out of range for uint64: %d' % i)
          return i
docs: Reads a varint from the stream, interprets this varint
          as an unsigned, 64-bit integer, and returns the integer.