ENH: Show column name in assert_frame_equal (#29218)

Co-authored-by: Joris Van den Bossche <[email protected]>

Author: moi90

pandas/_testing.py

@@ -1287,7 +1287,7 @@ def assert_frame_equal(
     >>> assert_frame_equal(df1, df2)
     Traceback (most recent call last):
     ...
-    AssertionError: Attributes of DataFrame.iloc[:, 1] are different
+    AssertionError: Attributes of DataFrame.iloc[:, 1] (column name="b") are different
 
     Attribute "dtype" are different
     [left]:  int64
@@ -1366,7 +1366,7 @@ def assert_frame_equal(
                 check_names=check_names,
                 check_datetimelike_compat=check_datetimelike_compat,
                 check_categorical=check_categorical,
-                obj=f"{obj}.iloc[:, {i}]",
+                obj=f'{obj}.iloc[:, {i}] (column name="{col}")',
             )
 
 

pandas/tests/util/test_assert_frame_equal.py

@@ -181,9 +181,9 @@ def test_frame_equal_columns_mismatch(obj_fixture):
 
 
 def test_frame_equal_block_mismatch(by_blocks_fixture, obj_fixture):
-    msg = """{obj}\\.iloc\\[:, 1\\] are different
+    msg = """{obj}\\.iloc\\[:, 1\\] \\(column name="B"\\) are different
 
-{obj}\\.iloc\\[:, 1\\] values are different \\(33\\.33333 %\\)
+{obj}\\.iloc\\[:, 1\\] \\(column name="B"\\) values are different \\(33\\.33333 %\\)
 \\[left\\]:  \\[4, 5, 6\\]
 \\[right\\]: \\[4, 5, 7\\]""".format(
         obj=obj_fixture
@@ -202,18 +202,18 @@ def test_frame_equal_block_mismatch(by_blocks_fixture, obj_fixture):
         (
             DataFrame({"A": ["á", "à", "ä"], "E": ["é", "è", "ë"]}),
             DataFrame({"A": ["á", "à", "ä"], "E": ["é", "è", "e̊"]}),
-            """{obj}\\.iloc\\[:, 1\\] are different
+            """{obj}\\.iloc\\[:, 1\\] \\(column name="E"\\) are different
 
-{obj}\\.iloc\\[:, 1\\] values are different \\(33\\.33333 %\\)
+{obj}\\.iloc\\[:, 1\\] \\(column name="E"\\) values are different \\(33\\.33333 %\\)
 \\[left\\]:  \\[é, è, ë\\]
 \\[right\\]: \\[é, è, e̊\\]""",
         ),
         (
             DataFrame({"A": ["á", "à", "ä"], "E": ["é", "è", "ë"]}),
             DataFrame({"A": ["a", "a", "a"], "E": ["e", "e", "e"]}),
-            """{obj}\\.iloc\\[:, 0\\] are different
+            """{obj}\\.iloc\\[:, 0\\] \\(column name="A"\\) are different
 
-{obj}\\.iloc\\[:, 0\\] values are different \\(100\\.0 %\\)
+{obj}\\.iloc\\[:, 0\\] \\(column name="A"\\) values are different \\(100\\.0 %\\)
 \\[left\\]:  \\[á, à, ä\\]
 \\[right\\]: \\[a, a, a\\]""",
         ),