code: def _join_keys_v1(left, right):
      
      if left.endswith(':') or '::' in left:
          raise ValueError("Can't join a left string ending in ':' or containing '::'")
      return u"{}::{}".format(_encode_v1(left), _encode_v1(right))
docs: Join two keys into a format separable by using _split_keys_v1.