code: def combine(beds, beds_sorted=False, postmerge=True):
      beds = copy.deepcopy(beds)
      for i,v in enumerate(beds):
          if type(v) == str:
              beds[i] = pbt.BedTool(v)
          if not beds_sorted:
              beds[i] = beds[i].sort()
      out = reduce(lambda x,y : x.cat(y, postmerge=False), beds)
      out = out.sort()
      if postmerge:
          out = out.merge()
      return out