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 ==.

4 files changed, 69 insertions, 11 deletions

diff --git a/Lib/test/list_tests.py b/Lib/test/list_tests.py
index 40316de..44bc2ae 100644
--- a/Lib/test/list_tests.py
+++ b/Lib/test/list_tests.py
@@ -7,6 +7,7 @@ import os
 from functools import cmp_to_key
 
 from test import support, seq_tests
+from test.support import ALWAYS_EQ, NEVER_EQ
 
 
 class CommonTest(seq_tests.CommonTest):
@@ -329,6 +330,20 @@ class CommonTest(seq_tests.CommonTest):
 
         self.assertRaises(TypeError, a.remove)
 
+        a = self.type2test([1, 2])
+        self.assertRaises(ValueError, a.remove, NEVER_EQ)
+        self.assertEqual(a, [1, 2])
+        a.remove(ALWAYS_EQ)
+        self.assertEqual(a, [2])
+        a = self.type2test([ALWAYS_EQ])
+        a.remove(1)
+        self.assertEqual(a, [])
+        a = self.type2test([ALWAYS_EQ])
+        a.remove(NEVER_EQ)
+        self.assertEqual(a, [])
+        a = self.type2test([NEVER_EQ])
+        self.assertRaises(ValueError, a.remove, ALWAYS_EQ)
+
         class BadExc(Exception):
             pass
 
diff --git a/Lib/test/seq_tests.py b/Lib/test/seq_tests.py
index 65b110e..1d9ad58 100644
--- a/Lib/test/seq_tests.py
+++ b/Lib/test/seq_tests.py
@@ -6,6 +6,7 @@ import unittest
 import sys
 import pickle
 from test import support
+from test.support import ALWAYS_EQ, NEVER_EQ
 
 # Various iterables
 # This is used for checking the constructor (here and in test_deque.py)
@@ -221,15 +222,15 @@ class CommonTest(unittest.TestCase):
         self.assertRaises(TypeError, u.__contains__)
 
     def test_contains_fake(self):
-        class AllEq:
-            # Sequences must use rich comparison against each item
-            # (unless "is" is true, or an earlier item answered)
-            # So instances of AllEq must be found in all non-empty sequences.
-            def __eq__(self, other):
-                return True
-            __hash__ = None # Can't meet hash invariant requirements
-        self.assertNotIn(AllEq(), self.type2test([]))
-        self.assertIn(AllEq(), self.type2test([1]))
+        # Sequences must use rich comparison against each item
+        # (unless "is" is true, or an earlier item answered)
+        # So ALWAYS_EQ must be found in all non-empty sequences.
+        self.assertNotIn(ALWAYS_EQ, self.type2test([]))
+        self.assertIn(ALWAYS_EQ, self.type2test([1]))
+        self.assertIn(1, self.type2test([ALWAYS_EQ]))
+        self.assertNotIn(NEVER_EQ, self.type2test([]))
+        self.assertNotIn(ALWAYS_EQ, self.type2test([NEVER_EQ]))
+        self.assertIn(NEVER_EQ, self.type2test([ALWAYS_EQ]))
 
     def test_contains_order(self):
         # Sequences must test in-order.  If a rich comparison has side
@@ -350,6 +351,11 @@ class CommonTest(unittest.TestCase):
         self.assertEqual(a.count(1), 3)
         self.assertEqual(a.count(3), 0)
 
+        self.assertEqual(a.count(ALWAYS_EQ), 9)
+        self.assertEqual(self.type2test([ALWAYS_EQ, ALWAYS_EQ]).count(1), 2)
+        self.assertEqual(self.type2test([ALWAYS_EQ, ALWAYS_EQ]).count(NEVER_EQ), 2)
+        self.assertEqual(self.type2test([NEVER_EQ, NEVER_EQ]).count(ALWAYS_EQ), 0)
+
         self.assertRaises(TypeError, a.count)
 
         class BadExc(Exception):
@@ -378,6 +384,11 @@ class CommonTest(unittest.TestCase):
         self.assertEqual(u.index(0, 3, 4), 3)
         self.assertRaises(ValueError, u.index, 2, 0, -10)
 
+        self.assertEqual(u.index(ALWAYS_EQ), 0)
+        self.assertEqual(self.type2test([ALWAYS_EQ, ALWAYS_EQ]).index(1), 0)
+        self.assertEqual(self.type2test([ALWAYS_EQ, ALWAYS_EQ]).index(NEVER_EQ), 0)
+        self.assertRaises(ValueError, self.type2test([NEVER_EQ, NEVER_EQ]).index, ALWAYS_EQ)
+
         self.assertRaises(TypeError, u.index)
 
         class BadExc(Exception):
diff --git a/Lib/test/support/__init__.py b/Lib/test/support/__init__.py
index c82037e..d34f2ef 100644
--- a/Lib/test/support/__init__.py
+++ b/Lib/test/support/__init__.py
@@ -113,7 +113,7 @@ __all__ = [
     "run_with_locale", "swap_item",
     "swap_attr", "Matcher", "set_memlimit", "SuppressCrashReport", "sortdict",
     "run_with_tz", "PGO", "missing_compiler_executable", "fd_count",
-    "ALWAYS_EQ", "LARGEST", "SMALLEST"
+    "ALWAYS_EQ", "NEVER_EQ", "LARGEST", "SMALLEST"
     ]
 
 class Error(Exception):
@@ -3115,6 +3115,17 @@ class _ALWAYS_EQ:
 
 ALWAYS_EQ = _ALWAYS_EQ()
 
+class _NEVER_EQ:
+    """
+    Object that is not equal to anything.
+    """
+    def __eq__(self, other):
+        return False
+    def __ne__(self, other):
+        return True
+
+NEVER_EQ = _NEVER_EQ()
+
 @functools.total_ordering
 class _LARGEST:
     """
diff --git a/Lib/test/test_iter.py b/Lib/test/test_iter.py
index 542b284..6aceda2 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)