code: def read_anchors(ac, qorder, sorder, minsize=0):
      
      all_anchors = defaultdict(list)
      nanchors = 0
      anchor_to_block = {}
  
      for a, b, idx in ac.iter_pairs(minsize=minsize):
          if a not in qorder or b not in sorder:
              continue
          qi, q = qorder[a]
          si, s = sorder[b]
          pair = (qi, si)
  
          all_anchors[(q.seqid, s.seqid)].append(pair)
          anchor_to_block[pair] = idx
          nanchors += 1
  
      logging.debug("A total of {0} anchors imported.".format(nanchors))
      assert nanchors == len(anchor_to_block)
  
      return all_anchors, anchor_to_block
docs: anchors file are just (geneA, geneB) pairs (with possible deflines)