only error if both keys and values are the same

README.rst

@@ -205,7 +205,7 @@ second usage. Save the result to a list if the result is needed multiple times.
 
 **B040**: Caught exception with call to ``add_note`` not used. Did you forget to ``raise`` it?
 
-**B041**: Repeated key in dictionary literal. The last value will override any previous values.
+**B041**: Repeated key-value pair in dictionary literal.
 
 Opinionated warnings
 ~~~~~~~~~~~~~~~~~~~~

bugbear.py

@@ -649,7 +649,7 @@ def visit_Dict(self, node) -> None:
         self.generic_visit(node)
 
     def check_for_b041(self, node) -> None:
-        # Complain if there are duplicate keys in a dictionary literal.
+        # Complain if there are duplicate key-value pairs in a dictionary literal.
         def convert_to_value(item):
             if isinstance(item, ast.Constant):
                 return item.value
@@ -668,9 +668,13 @@ def convert_to_value(item):
         ]
         for key in duplicate_keys:
             key_indices = [i for i, i_key in enumerate(keys) if i_key == key]
-            for key_index in key_indices:
-                key_node = node.keys[key_index]
-                self.errors.append(B041(key_node.lineno, key_node.col_offset))
+            seen = set()
+            for index in key_indices:
+                value = convert_to_value(node.values[index])
+                if value in seen:
+                    key_node = node.keys[index]
+                    self.errors.append(B041(key_node.lineno, key_node.col_offset))
+                seen.add(value)
 
     def check_for_b005(self, node) -> None:
         if isinstance(node, ast.Import):
@@ -2368,8 +2372,7 @@ def visit_Lambda(self, node) -> None:
 
 B041 = Error(
     message=(
-        "B041 Repeated key in dictionary literal. The last value will override "
-        "any previous values."
+        "B041 Repeated key-value pair in dictionary literal."
     )
 )
 

tests/b041.py

@@ -1,84 +1,24 @@
-# Simple case
-{'yes': 1, 'yes': 2}  # error
-
-# Duplicate keys with bytes vs unicode in Python 3
-{b'a': 1, u'a': 2}  # error
-{1: b'a', 1: u'a'}  # error
-
-# Duplicate keys with bytes vs unicode in Python 2
-{b'a': 1, u'a': 2}  # error
-
-# Duplicate values in Python 2
-{1: b'a', 1: u'a'}  # error
-
-# Multiple duplicate keys
-{'yes': 1, 'yes': 2, 'no': 2, 'no': 3}  # error
-
-# Duplicate keys in function call
-def f(thing):
-    pass
-f({'yes': 1, 'yes': 2})  # error
-
-# Duplicate keys in lambda function
-(lambda x: {(0, 1): 1, (0, 1): 2})  # error
-
-# Duplicate keys with tuples
-{(0, 1): 1, (0, 1): 2}  # error
-
-# Duplicate keys with int and float
-{1: 1, 1.0: 2}  # error
-
-# Duplicate keys with booleans
-{True: 1, True: 2}  # error
-
-# Duplicate keys with None
-{None: 1, None: 2}  # error
-
-# Duplicate keys with variables
-a = 1
-{a: 1, a: 2}  # error
-
-# Duplicate values with variables
-a = 1
-b = 2
-{1: a, 1: b}  # error
-
-# Duplicate values with same variable value
 a = 1
+test = {'yes': 1, 'yes': 1}
+test = {'yes': 1, 'yes': 1, 'no': 2, 'no': 2}
+test = {'yes': 1, 'yes': 1, 'yes': 1}
+test = {1: 1, 1.0: 1}
+test = {True: 1, True: 1}
+test = {None: 1, None: 1}
+test = {a: a, a: a}
+
+# no error if either keys or values are different
+test = {'yes': 1, 'yes': 2}
+test = {1: 1, 2: 1}
+test = {(0, 1): 1, (0, 2): 1}
+test = {(0, 1): 1, (0, 1): 2}
 b = 1
-{1: a, 1: b}  # error
-
-# Duplicate keys with same values
-{'yes': 1, 'yes': 1}  # error
-
-# Non-duplicate keys
-{'yes': 1, 'no': 2}  # safe
-
-# Non-duplicate keys with tuples having the same first element
-{(0, 1): 1, (0, 2): 1}  # safe
-
-# Non-duplicate keys in function call
-def test_func(thing):
-    pass
-test_func({True: 1, None: 2, False: 1})  # safe
-
-# Non-duplicate keys with bool and None
-{True: 1, None: 2, False: 1}  # safe
-
-# Non-duplicate keys with different ints
-{1: 1, 2: 1}  # safe
-
-# Duplicate keys with differently-named variables
-test = 'yes'
-rest = 'yes'
-{test: 1, rest: 2}  # safe
-
-# Non-duplicate tuple keys
-{(0, 1): 1, (0, 2): 1}  # safe
-
-# Duplicate keys with instance attributes
+test = {a: a, b: a}
+test = {a: a, a: b}
 class TestClass:
     pass
 f = TestClass()
 f.a = 1
-{f.a: 1, f.a: 1}  # safe
+test = {f.a: 1, f.a: 1}
+
+

tests/test_bugbear.py

@@ -48,6 +48,7 @@
     B037,
     B039,
     B040,
+    B041,
     B901,
     B902,
     B903,
@@ -666,6 +667,23 @@ def test_b040(self) -> None:
         )
         self.assertEqual(errors, expected)
 
+    def test_b041(self) -> None:
+        filename = Path(__file__).absolute().parent / "b041.py"
+        bbc = BugBearChecker(filename=str(filename))
+        errors = list(bbc.run())
+        expected = self.errors(
+            B041(2, 18),
+            B041(3, 18),
+            B041(3, 37),
+            B041(4, 18),
+            B041(4, 28),
+            B041(5, 14),
+            B041(6, 17),
+            B041(7, 17),
+            B041(8, 14),
+        )
+        self.assertEqual(errors, expected)
+
     def test_b908(self):
         filename = Path(__file__).absolute().parent / "b908.py"
         bbc = BugBearChecker(filename=str(filename))