dont set name

Author: MarcoGorelli

pandas/core/groupby/generic.py

@@ -401,7 +401,8 @@ def _wrap_applied_output(
                 not_indexed_same=not_indexed_same,
                 is_transform=is_transform,
             )
-            result.name = self.obj.name
+            if isinstance(result, Series):
+                result.name = self.obj.name
             return result
         else:
             # GH #6265 #24880

pandas/core/groupby/groupby.py

@@ -1177,8 +1177,7 @@ def reset_identity(values):
             result = concat(values, axis=self.axis)
 
         name = self.obj.name if self.obj.ndim == 1 else self._selection
-        if isinstance(result, Series) and name is not None:
-
+        if isinstance(result, Series) and result.name is None and name is not None:
             result.name = name
 
         return result

pandas/tests/groupby/test_apply.py

@@ -334,6 +334,7 @@ def f(piece):
     result = grouped.apply(f)
 
     assert isinstance(result, DataFrame)
+    assert not hasattr(result, "name")
     tm.assert_index_equal(result.index, ts.index)
 
 
@@ -1316,7 +1317,6 @@ def test_result_name_when_one_group(name):
     ser = Series([1, 2], name=name)
     result = ser.groupby(["a", "a"], group_keys=False).apply(lambda x: x)
     expected = Series([1, 2], name=name)
-
     tm.assert_series_equal(result, expected)