[Python-checkins] bpo-37158: Simplify and speed-up statistics.fmean() (GH-13832) (GH-13843)

[Raymond Hettinger]

https://github.com/python/cpython/commit/9ddb77741e041966d64739353393bcba33cc3bdd
commit: 9ddb77741e041966d64739353393bcba33cc3bdd
branch: 3.8
author: Miss Islington (bot) <31488909+miss-islington at users.noreply.github.com>
committer: Raymond Hettinger <rhettinger at users.noreply.github.com>
date: 2019-06-05T08:18:13-07:00
summary:

bpo-37158: Simplify and speed-up statistics.fmean() (GH-13832) (GH-13843)

(cherry picked from commit 6c01ebcc0dfc6be22950fabb46bdc10dcb6202c9)

Co-authored-by: Raymond Hettinger <rhettinger at users.noreply.github.com>

files:
A Misc/NEWS.d/next/Library/2019-06-04-22-25-38.bpo-37158.JKm15S.rst
M Lib/statistics.py

diff --git a/Lib/statistics.py b/Lib/statistics.py
index 012845b8d2ef..5be70e5ebf4e 100644
--- a/Lib/statistics.py
+++ b/Lib/statistics.py
@@ -320,11 +320,11 @@ def fmean(data):
     except TypeError:
         # Handle iterators that do not define __len__().
         n = 0
-        def count(x):
+        def count(iterable):
             nonlocal n
-            n += 1
-            return x
-        total = fsum(map(count, data))
+            for n, x in enumerate(iterable, start=1):
+                yield x
+        total = fsum(count(data))
     else:
         total = fsum(data)
     try:
diff --git a/Misc/NEWS.d/next/Library/2019-06-04-22-25-38.bpo-37158.JKm15S.rst b/Misc/NEWS.d/next/Library/2019-06-04-22-25-38.bpo-37158.JKm15S.rst
new file mode 100644
index 000000000000..4a5ec4122f94
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-06-04-22-25-38.bpo-37158.JKm15S.rst
@@ -0,0 +1 @@
+Speed-up statistics.fmean() by switching from a function to a generator.