code: def forever(it):
      
      while True:
          # generator 두번쨰 iteration 무한 루프 방지
          i = iter(it)
          try:
              yield i.next()
          except StopIteration:
              raise StopIteration
          while True:
              try:
                  yield i.next()
              except StopIteration:
                  break
docs: forever
      todo : add example