code: def restore(delta, which):
      r
      try:
          tag = {1: "- ", 2: "+ "}[int(which)]
      except KeyError:
          raise ValueError, ('unknown delta choice (must be 1 or 2): %r'
                             % which)
      prefixes = ("  ", tag)
      for line in delta:
          if line[:2] in prefixes:
              yield line[2:]
docs: r"""
      Generate one of the two sequences that generated a delta.
  
      Given a `delta` produced by `Differ.compare()` or `ndiff()`, extract
      lines originating from file 1 or 2 (parameter `which`), stripping off line
      prefixes.
  
      Examples:
  
      >>> diff = ndiff('one\ntwo\nthree\n'.splitlines(1),
      ...              'ore\ntree\nemu\n'.splitlines(1))
      >>> diff = list(diff)
      >>> print ''.join(restore(diff, 1)),
      one
      two
      three
      >>> print ''.join(restore(diff, 2)),
      ore
      tree
      emu