Merge in r68394 fixing itertools.permutations() and combinations().

1 files changed, 12 insertions, 3 deletions

diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
index b384cc8..db10b6d 100644
--- a/Doc/library/itertools.rst
+++ b/Doc/library/itertools.rst
@@ -104,7 +104,9 @@ loops that truncate the stream.
             # combinations(range(4), 3) --> 012 013 023 123
             pool = tuple(iterable)
             n = len(pool)
-            indices = range(r)
+            if r > n:
+                return
+            indices = list(range(r))
             yield tuple(pool[i] for i in indices)
             while 1:
                 for i in reversed(range(r)):
@@ -128,6 +130,8 @@ loops that truncate the stream.
                 if sorted(indices) == list(indices):
                     yield tuple(pool[i] for i in indices)
 
+   The number of items returned is ``n! / r! / (n-r)!`` when ``0 <= r <= n``
+   or zero when ``r > n``.
 
 .. function:: count([n])
 
@@ -325,7 +329,9 @@ loops that truncate the stream.
             pool = tuple(iterable)
             n = len(pool)
             r = n if r is None else r
-            indices = range(n)
+            if r > n:
+                return
+            indices = list(range(n))
             cycles = range(n, n-r, -1)
             yield tuple(pool[i] for i in indices[:r])
             while n:
@@ -354,6 +360,8 @@ loops that truncate the stream.
                 if len(set(indices)) == r:
                     yield tuple(pool[i] for i in indices)
 
+   The number of items returned is ``n! / (n-r)!`` when ``0 <= r <= n``
+   or zero when ``r > n``.
 
 .. function:: product(*iterables[, repeat])
 
@@ -593,7 +601,8 @@ which incur interpreter overhead.
        return (d for d, s in zip(data, selectors) if s)
 
    def combinations_with_replacement(iterable, r):
-       "combinations_with_replacement('ABC', 3) --> AA AB AC BB BC CC"
+       "combinations_with_replacement('ABC', 2) --> AA AB AC BB BC CC"
+       # number items returned:  (n+r-1)! / r! / (n-1)!
        pool = tuple(iterable)
        n = len(pool)
        indices = [0] * r