Appends flags registered in another FlagValues instance.

    Args:
      flag_values: FlagValues, the FlagValues instance from which to copy flags.

def append_flag_values(self, flag_values):
    """Appends flags registered in another FlagValues instance.

    Args:
      flag_values: FlagValues, the FlagValues instance from which to copy flags.
    """
    for flag_name, flag in six.iteritems(flag_values._flags()):  # pylint: disable=protected-access
      # Each flags with short_name appears here twice (once under its
      # normal name, and again with its short name).  To prevent
      # problems (DuplicateFlagError) with double flag registration, we
      # perform a check to make sure that the entry we're looking at is
      # for its normal name.
      if flag_name == flag.name:
        try:
          self[flag_name] = flag
        except _exceptions.DuplicateFlagError:
          raise _exceptions.DuplicateFlagError.from_flag(
              flag_name, self, other_flag_values=flag_values)