sliding_window() recipe: Raise ValueError for non-positive window siz…

…es. Add more tests. (GH-105403)

Doc/library/itertools.rst

@@ -929,9 +929,7 @@ which incur interpreter overhead.
  def sliding_window(iterable, n):
  # sliding_window('ABCDEFG', 4) --> ABCD BCDE CDEF DEFG
  it = iter(iterable)
- window = collections.deque(islice(it, n), maxlen=n)
- if len(window) == n:
- yield tuple(window)
+ window = collections.deque(islice(it, n-1), maxlen=n)
  for x in it:
  window.append(x)
  yield tuple(window)
@@ -1420,8 +1418,34 @@ The following recipes have a more mathematical flavor:
  >>> list(grouper('abcdefg', n=3, incomplete='ignore'))
  [('a', 'b', 'c'), ('d', 'e', 'f')]
 
+ >>> list(sliding_window('ABCDEFG', 1))
+ [('A',), ('B',), ('C',), ('D',), ('E',), ('F',), ('G',)]
+ >>> list(sliding_window('ABCDEFG', 2))
+ [('A', 'B'), ('B', 'C'), ('C', 'D'), ('D', 'E'), ('E', 'F'), ('F', 'G')]
+ >>> list(sliding_window('ABCDEFG', 3))
+ [('A', 'B', 'C'), ('B', 'C', 'D'), ('C', 'D', 'E'), ('D', 'E', 'F'), ('E', 'F', 'G')]
  >>> list(sliding_window('ABCDEFG', 4))
  [('A', 'B', 'C', 'D'), ('B', 'C', 'D', 'E'), ('C', 'D', 'E', 'F'), ('D', 'E', 'F', 'G')]
+ >>> list(sliding_window('ABCDEFG', 5))
+ [('A', 'B', 'C', 'D', 'E'), ('B', 'C', 'D', 'E', 'F'), ('C', 'D', 'E', 'F', 'G')]
+ >>> list(sliding_window('ABCDEFG', 6))
+ [('A', 'B', 'C', 'D', 'E', 'F'), ('B', 'C', 'D', 'E', 'F', 'G')]
+ >>> list(sliding_window('ABCDEFG', 7))
+ [('A', 'B', 'C', 'D', 'E', 'F', 'G')]
+ >>> list(sliding_window('ABCDEFG', 8))
+ []
+ >>> try:
+ ... list(sliding_window('ABCDEFG', -1))
+ ... except ValueError:
+ ... 'zero or negative n not supported'
+ ...
+ 'zero or negative n not supported'
+ >>> try:
+ ... list(sliding_window('ABCDEFG', 0))
+ ... except ValueError:
+ ... 'zero or negative n not supported'
+ ...
+ 'zero or negative n not supported'
 
  >>> list(roundrobin('abc', 'd', 'ef'))
  ['a', 'd', 'e', 'b', 'f', 'c']