code: def append_var_uint64(self, unsigned_value):
          
          if not 0 <= unsigned_value <= wire_format.UINT64_MAX:
              raise errors.EncodeError('Value out of range: %d' % unsigned_value)
          while True:
              bits = unsigned_value & 0x7f
              unsigned_value >>= 7
              if unsigned_value:
                  bits |= 0x80
              self._buffer.append(bits)
              if not unsigned_value:
                  break
docs: Appends an unsigned 64-bit integer to the internal buffer,
          encoded as a varint.