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bpo-40855: Fix ignored mu and xbar parameters (GH-20835) (GH-20863)
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3 files changed

+18
-2
lines changed

3 files changed

+18
-2
lines changed

Lib/statistics.py

Lines changed: 4 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -682,8 +682,10 @@ def _ss(data, c=None):
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calculated from ``c`` as given. Use the second case with care, as it can
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lead to garbage results.
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"""
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if c is None:
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c = mean(data)
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if c is not None:
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T, total, count = _sum((x-c)**2 for x in data)
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return (T, total)
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c = mean(data)
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T, total, count = _sum((x-c)**2 for x in data)
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# The following sum should mathematically equal zero, but due to rounding
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# error may not.

Lib/test/test_statistics.py

Lines changed: 12 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2029,6 +2029,10 @@ def test_decimals(self):
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self.assertEqual(result, exact)
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self.assertIsInstance(result, Decimal)
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2032+
def test_center_not_at_mean(self):
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data = (1.0, 2.0)
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self.assertEqual(self.func(data), 0.5)
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self.assertEqual(self.func(data, xbar=2.0), 1.0)
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class TestPStdev(VarianceStdevMixin, NumericTestCase):
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# Tests for population standard deviation.
@@ -2041,6 +2045,11 @@ def test_compare_to_variance(self):
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expected = math.sqrt(statistics.pvariance(data))
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self.assertEqual(self.func(data), expected)
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2048+
def test_center_not_at_mean(self):
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# See issue: 40855
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data = (3, 6, 7, 10)
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self.assertEqual(self.func(data), 2.5)
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self.assertEqual(self.func(data, mu=0.5), 6.5)
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class TestStdev(VarianceStdevMixin, NumericTestCase):
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# Tests for sample standard deviation.
@@ -2058,6 +2067,9 @@ def test_compare_to_variance(self):
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expected = math.sqrt(statistics.variance(data))
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self.assertEqual(self.func(data), expected)
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2070+
def test_center_not_at_mean(self):
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data = (1.0, 2.0)
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self.assertEqual(self.func(data, xbar=2.0), 1.0)
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class TestGeometricMean(unittest.TestCase):
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Lines changed: 2 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,2 @@
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The standard deviation and variance functions in the statistics module were
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ignoring their mu and xbar arguments.

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