Merge nonstring columns

doc/source/whatsnew/v1.5.0.rst

@@ -511,6 +511,12 @@ Strings
 - Bug in :meth:`str.startswith` and :meth:`str.endswith` when using other series as parameter _pat_. Now raises ``TypeError`` (:issue:`3485`)
 -
 
+Merge
+^^^^^^^
+- Bug in :meth:`merge` supports user-defined types merge with identical columns
+-
+
+
 Interval
 ^^^^^^^^
 - Bug in :meth:`IntervalArray.__setitem__` when setting ``np.nan`` into an integer-backed array raising ``ValueError`` instead of ``TypeError`` (:issue:`45484`)

pandas/core/reshape/merge.py

@@ -2383,15 +2383,18 @@ def renamer(x, suffix):
 
         Parameters
         ----------
-        x : original column name
+        x : original column
         suffix : str or None
 
         Returns
         -------
-        x : renamed column name
+        x : renamed column
         """
         if x in to_rename and suffix is not None:
-            return f"{x}{suffix}"
+            try:
+                return x + suffix
+            except TypeError:
+                return f"{x}{suffix}"
         return x
 
     lrenamer = partial(renamer, suffix=lsuffix)

pandas/tests/reshape/merge/test_merge.py

@@ -2669,3 +2669,28 @@ def test_merge_different_index_names():
     result = merge(left, right, left_on="c", right_on="d")
     expected = DataFrame({"a_x": [1], "a_y": 1})
     tm.assert_frame_equal(result, expected)
+
+
+def test_merge_complex_column():
+    # GH#46885
+    class Column:
+        def __init__(self, name):
+            self.name = name
+
+        def __eq__(self, other):
+            return other.name == self.name
+
+        def __hash__(self):
+            return hash(self.name)
+
+        def __add__(self, other):
+            return Column(name=f"{self.name}@{other}")
+
+    merged_column = Column(name="Z")
+    left = DataFrame([[1, 2]], columns=[merged_column, "X"])
+    right = DataFrame([[1, 6]], columns=[merged_column, "Y"])
+    result = merge(left, right, left_index=True, right_index=True)
+    expected = DataFrame(
+        [[1, 2, 1, 6]], columns=[Column("Z@_x"), "X", Column("Z@_y"), "Y"]
+    )
+    tm.assert_frame_equal(result, expected)