Add running_mean recipe to demonstrate accumulate and count

Author: rhettinger

Doc/library/itertools.rst

@@ -845,7 +845,7 @@ and :term:`generators <generator>` which incur interpreter overhead.
    from contextlib import suppress
    from functools import reduce
    from math import comb, isqrt, prod, sumprod
-   from operator import getitem, is_not, itemgetter, mul, neg
+   from operator import getitem, is_not, itemgetter, mul, neg, truediv
 
    # ==== Basic one liners ====
 
@@ -862,6 +862,11 @@ and :term:`generators <generator>` which incur interpreter overhead.
        "Return function(0), function(1), ..."
        return map(function, count(start))
 
+   def running_mean(iterable):
+       "Yield the cumulative arithmetic mean."
+       # running_mean([8.5, 9.5, 7.5, 7.0]) -> 8.5 9.0 8.5 8.0
+       return map(truediv, accumulate(iterable), count(1))
+
    def repeatfunc(function, times=None, *args):
        "Repeat calls to a function with specified arguments."
        if times is None:
@@ -1234,6 +1239,10 @@ and :term:`generators <generator>` which incur interpreter overhead.
     [0, 2, 4, 6]
 
 
+    >>> list(running_median([8.5, 9.5, 7.5, 7.0]))
+   [8.5, 9.0, 8.5, 8.0]
+
+
     >>> for _ in loops(5):
     ...     print('hi')
     ...