code: def all_pairs(seq1, seq2=None):
      
      if seq2 is None: seq2 = seq1
      for item1 in seq1:
          for item2 in seq2:
              yield (item1, item2)
docs: Yields all pairs drawn from ``seq1`` and ``seq2``.
  
      If ``seq2`` is ``None``, ``seq2 = seq1``.
  
          >>> stop_at.ed(all_pairs(xrange(100000), xrange(100000)), 8)
          ((0, 0), (0, 1), (0, 2), (0, 3), (0, 4), (0, 5), (0, 6), (0, 7))