From 59b015844dd4fdbd47ae32903f8fabaadc8aaa4a Mon Sep 17 00:00:00 2001
From: Drew Winstel <drew@defna.org>
Date: Wed, 29 May 2024 08:06:09 -0500
Subject: [PATCH] =?UTF-8?q?=F0=9F=90=8D=20Use=20the=20stdlib=20for=20our?=
 =?UTF-8?q?=20score=20statistics?=
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Python 3.4 [introduced](https://docs.python.org/3/library/statistics.html)
the `statistics` module into the standard library. Let's use that
instead of calculating our own simply for the sake of not reinventing
the wheel.
---
 grants/models.py | 21 +++++++++------------
 1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/grants/models.py b/grants/models.py
index 3ce4ce6..41e6897 100644
--- a/grants/models.py
+++ b/grants/models.py
@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+from statistics import mean, variance, stdev
+
 from django.db import models
 from urlman import Urls
 
@@ -141,24 +143,19 @@ def average_score(self):
         scores = [s.score for s in self.scores.all() if s.score]
         if not scores:
             return None
-        else:
-            return sum(scores) / float(len(scores))
+        return mean(scores)
 
     def variance(self):
         data = [s.score for s in self.scores.all() if s.score]
-        n = len(data)
-        if n == 0:
-            return 0
-        c = sum(data) / float(len(data))
-        if n < 2:
+        if not data:
             return 0
-        ss = sum((x - c) ** 2 for x in data)
-        ss -= sum((x - c) for x in data) ** 2 / len(data)
-        assert not ss < 0, "negative sum of square deviations: %f" % ss
-        return ss / (n - 1)
+        return variance(data)
 
     def stdev(self):
-        return self.variance() ** 0.5
+        data = [s.score for s in self.scores.all() if s.score]
+        if not data:
+            return 0
+        return stdev(data)
 
 
 class Allocation(models.Model):