Add and update itertools recipes.

Doc/library/itertools.rst

@@ -455,7 +455,7 @@ loops that truncate the stream.
        def product(*args, repeat=1):
            # product('ABCD', 'xy') --> Ax Ay Bx By Cx Cy Dx Dy
            # product(range(2), repeat=3) --> 000 001 010 011 100 101 110 111
-           pools = map(tuple, args) * repeat
+           pools = [tuple(pool) for pool in args] * repeat
            result = [[]]
            for pool in pools:
                result = [x+[y] for x in result for y in pool]
@@ -617,7 +617,8 @@ which incur interpreter overhead.
        return sum(map(operator.mul, vec1, vec2))
 
    def flatten(listOfLists):
-       return list(chain.from_iterable(listOfLists))
+       "Flatten one level of nesting"
+       return chain.from_iterable(listOfLists)
 
    def repeatfunc(func, times=None, *args):
        """Repeat calls to func with specified arguments.
@@ -703,6 +704,27 @@ which incur interpreter overhead.
        except exception:
            pass
 
+   def random_product(*args, repeat=1):
+       "Random selection from itertools.product(*args, **kwds)"
+       pools = [tuple(pool) for pool in args] * repeat
+       return [random.choice(pool) for pool in pools]
+
+   def random_permuation(iterable, r=None):
+       "Random selection from itertools.permutations(iterable, r)"
+       pool = tuple(iterable)
+       r = len(pool) if r is None else r
+       return random.sample(pool, r)
+
+   def random_combination(iterable, r):
+       "Random selection from itertools.combinations(iterable, r)"
+       pool = tuple(iterable)
+       return sorted(random.sample(pool, r), key=pool.index)
+
+   def random_combination_with_replacement(iterable, r):
+       "Random selection from itertools.combinations_with_replacement(iterable, r)"
+       pool = tuple(iterable)
+       return sorted(map(random.choice, repeat(pool, r)), key=pool.index)
+
 Note, many of the above recipes can be optimized by replacing global lookups
 with local variables defined as default values.  For example, the
 *dotproduct* recipe can be written as::