Add itertools.combinations().
diff --git a/Doc/library/itertools.rst b/Doc/library/itertools.rst
index c8f6e33..6dc19a1 100644
--- a/Doc/library/itertools.rst
+++ b/Doc/library/itertools.rst
@@ -97,21 +97,21 @@
def combinations(iterable, r):
pool = tuple(iterable)
- if pool:
- n = len(pool)
- vec = range(r)
- yield tuple(pool[i] for i in vec)
- while 1:
- for i in reversed(range(r)):
- if vec[i] == i + n-r:
- continue
- vec[i] += 1
- for j in range(i+1, r):
- vec[j] = vec[j-1] + 1
- yield tuple(pool[i] for i in vec)
- break
- else:
- return
+ n = len(pool)
+ assert 0 <= r <= n
+ vec = range(r)
+ yield tuple(pool[i] for i in vec)
+ while 1:
+ for i in reversed(range(r)):
+ if vec[i] == i + n-r:
+ continue
+ vec[i] += 1
+ for j in range(i+1, r):
+ vec[j] = vec[j-1] + 1
+ yield tuple(pool[i] for i in vec)
+ break
+ else:
+ return
.. versionadded:: 2.6