gh-118476: update the example implementation for islice in docs

Doc/library/itertools.rst

@@ -504,24 +504,20 @@ loops that truncate the stream.
  # islice('ABCDEFG', 2, None) → C D E F G
  # islice('ABCDEFG', 0, None, 2) → A C E G
  s = slice(*args)
- start, stop, step = s.start or 0, s.stop or sys.maxsize, s.step or 1
- it = iter(range(start, stop, step))
- try:
-  nexti = next(it)
- except StopIteration:
- # Consume *iterable* up to the *start* position.
- for i, element in zip(range(start), iterable):
-  pass
+ start = s.start if s.start is not None else 0
+ stop = s.stop
+ step = s.step if s.step is not None else 1
+ it = iter(iterable)
+ for _ in zip(range(start), it):
+ # Consume up to *start* position
+ pass
+ if stop is not None and stop <= start:
  return
- try:
- for i, element in enumerate(iterable):
- if i == nexti:
- yield element
- nexti = next(it)
- except StopIteration:
- # Consume to *stop*.
- for i, element in zip(range(i + 1, stop), iterable):
- pass
+ for i, element in enumerate(it, start):
+ if (i - start) % step == 0:
+ yield element
+ if stop is not None and i + 1 >= stop:
+ return
 
 
 .. function:: pairwise(iterable)