Backport PR #31036: BUG: AssertionError on Series.append(DataFrame) fix #30975 (#31267)

Co-authored-by: Harshavardhan Bachina <[email protected]>

Author: 2 people

pandas/tests/series/methods/test_append.py

@@ -61,6 +61,16 @@ def test_append_tuples(self):
 
         tm.assert_series_equal(expected, result)
 
+    def test_append_dataframe_regression(self):
+        # GH 30975
+        df = pd.DataFrame({"A": [1, 2]})
+        result = df.A.append([df])
+        expected = pd.DataFrame(
+            {0: [1.0, 2.0, None, None], "A": [None, None, 1.0, 2.0]}, index=[0, 1, 0, 1]
+        )
+
+        tm.assert_frame_equal(expected, result)
+
 
 class TestSeriesAppendWithDatetimeIndex:
     def test_append(self):