bpo-38521: Fix error in NormalDist.__eq__() (GH-16840) (GH-16842)

(cherry picked from commit 5eabec0)

Co-authored-by: Raymond Hettinger <[email protected]>

Author: miss-islington

Lib/statistics.py

@@ -1092,7 +1092,7 @@ def __eq__(x1, x2):
         "Two NormalDist objects are equal if their mu and sigma are both equal."
         if not isinstance(x2, NormalDist):
             return NotImplemented
-        return (x1._mu, x2._sigma) == (x2._mu, x2._sigma)
+        return x1._mu == x2._mu and x1._sigma == x2._sigma
 
     def __hash__(self):
         "NormalDist objects hash equal if their mu and sigma are both equal."

Lib/test/test_statistics.py

@@ -2651,9 +2651,13 @@ def test_equality(self):
         nd2 = NormalDist(2, 4)
         nd3 = NormalDist()
         nd4 = NormalDist(2, 4)
+        nd5 = NormalDist(2, 8)
+        nd6 = NormalDist(8, 4)
         self.assertNotEqual(nd1, nd2)
         self.assertEqual(nd1, nd3)
         self.assertEqual(nd2, nd4)
+        self.assertNotEqual(nd2, nd5)
+        self.assertNotEqual(nd2, nd6)
 
         # Test NotImplemented when types are different
         class A:

Misc/NEWS.d/next/Library/2019-10-18-13-57-31.bpo-38521.U-7aaM.rst

@@ -0,0 +1 @@
+Fixed erroneous equality comparison in statistics.NormalDist().