bpo-37648: Fixed minor inconsistency in some __contains__. (GH-14904)

The collection's item is now always at the left and
the needle is on the right of ==.

1 files changed, 22 insertions, 1 deletions

diff --git a/Lib/test/test_iter.py b/Lib/test/test_iter.py
index 542b28419e2..6aceda23e9b 100644
--- a/Lib/test/test_iter.py
+++ b/Lib/test/test_iter.py
@@ -3,7 +3,7 @@
 import sys
 import unittest
 from test.support import run_unittest, TESTFN, unlink, cpython_only
-from test.support import check_free_after_iterating
+from test.support import check_free_after_iterating, ALWAYS_EQ, NEVER_EQ
 import pickle
 import collections.abc
 
@@ -41,6 +41,14 @@ class IteratingSequenceClass:
     def __iter__(self):
         return BasicIterClass(self.n)
 
+class IteratorProxyClass:
+    def __init__(self, i):
+        self.i = i
+    def __next__(self):
+        return next(self.i)
+    def __iter__(self):
+        return self
+
 class SequenceClass:
     def __init__(self, n):
         self.n = n
@@ -50,6 +58,12 @@ class SequenceClass:
         else:
             raise IndexError
 
+class SequenceProxyClass:
+    def __init__(self, s):
+        self.s = s
+    def __getitem__(self, i):
+        return self.s[i]
+
 class UnlimitedSequenceClass:
     def __getitem__(self, i):
         return i
@@ -635,6 +649,13 @@ class TestCase(unittest.TestCase):
             for i in "abc", -1, 5, 42.42, (3, 4), [], {1: 1}, 3-12j, sc5:
                 self.assertNotIn(i, sc5)
 
+        self.assertIn(ALWAYS_EQ, IteratorProxyClass(iter([1])))
+        self.assertIn(ALWAYS_EQ, SequenceProxyClass([1]))
+        self.assertNotIn(ALWAYS_EQ, IteratorProxyClass(iter([NEVER_EQ])))
+        self.assertNotIn(ALWAYS_EQ, SequenceProxyClass([NEVER_EQ]))
+        self.assertIn(NEVER_EQ, IteratorProxyClass(iter([ALWAYS_EQ])))
+        self.assertIn(NEVER_EQ, SequenceProxyClass([ALWAYS_EQ]))
+
         self.assertRaises(TypeError, lambda: 3 in 12)
         self.assertRaises(TypeError, lambda: 3 not in map)