GH 30975-Fix for Series.append(DataFrame)

Author: hvardhan20

pandas/core/series.py

@@ -2538,6 +2538,9 @@ def append(self, to_append, ignore_index=False, verify_integrity=False) -> "Seri
             to_concat = [self]
             to_concat.extend(to_append)
         else:
+            if not isinstance(to_append, type(self)):
+                msg = f"to_append should be a Series or list/tuple of Series, got {type(to_append)}"
+                raise TypeError(msg)
             to_concat = [self, to_append]
         return self._ensure_type(
             concat(

pandas/tests/series/methods/test_append.py

@@ -61,6 +61,15 @@ def test_append_tuples(self):
 
         tm.assert_series_equal(expected, result)
 
+    def test_append_dataframe(self):
+        # GH 30975
+        df = pd.DataFrame({"A": [1, 2], "B": [3, 4]})
+        df2 = pd.DataFrame({"C": [5, 6], "D": [7, 8]})
+
+        expected = pd.Series(pd.concat([df.A, df2.D]))
+        result = df.A.append(df2.D)
+
+        tm.assert_series_equal(expected, result)
 
 class TestSeriesAppendWithDatetimeIndex:
     def test_append(self):