code: def sort_csv(in_file):
      out_file = "%s.sort" % in_file
      if not (os.path.exists(out_file) and os.path.getsize(out_file) > 0):
          cl = ["sort", "-k", "1,1", in_file]
          with open(out_file, "w") as out_handle:
              child = subprocess.Popen(cl, stdout=out_handle)
              child.wait()
      return out_file