def CheckPrereq(self):
    """Check prerequisites.

    This checks that we have the given tag.

    """
    TagsLU.CheckPrereq(self)
    for tag in self.op.tags:
      objects.TaggableObject.ValidateTag(tag)
    del_tags = frozenset(self.op.tags)
    cur_tags = self.target.GetTags()

    diff_tags = cur_tags - del_tags
    if diff_tags:
      diff_names = ("'%s'" % i for i in sorted(diff_tags))
      raise errors.OpPrereqError("Tag(s) %s not found" %
                                 (utils.CommaJoin(diff_names), ),
                                 errors.ECODE_NOENT)
dataset/ETHPy150Open ganeti/ganeti/lib/cmdlib/tags.py/LUTagsDel.CheckPrereq/swapped operands of `-`