BUG: Appending empty list to DataFrame #28769 (#28834)

Author: asishm

doc/source/whatsnew/v1.0.0.rst

@@ -465,6 +465,7 @@ Other
 - :meth:`Series.append` will no longer raise a ``TypeError`` when passed a tuple of ``Series`` (:issue:`28410`)
 - :meth:`SeriesGroupBy.value_counts` will be able to handle the case even when the :class:`Grouper` makes empty groups (:issue: 28479)
 - Fix corrupted error message when calling ``pandas.libs._json.encode()`` on a 0d array (:issue:`18878`)
+- Bug in :meth:`DataFrame.append` that raised ``IndexError`` when appending with empty list (:issue:`28769`)
 - Fix :class:`AbstractHolidayCalendar` to return correct results for
   years after 2030 (now goes up to 2200) (:issue:`27790`)
 

pandas/core/frame.py

@@ -6943,10 +6943,13 @@ def append(self, other, ignore_index=False, verify_integrity=False, sort=None):
             other = other._convert(datetime=True, timedelta=True)
             if not self.columns.equals(combined_columns):
                 self = self.reindex(columns=combined_columns)
-        elif isinstance(other, list) and not isinstance(other[0], DataFrame):
-            other = DataFrame(other)
-            if (self.columns.get_indexer(other.columns) >= 0).all():
-                other = other.reindex(columns=self.columns)
+        elif isinstance(other, list):
+            if not other:
+                pass
+            elif not isinstance(other[0], DataFrame):
+                other = DataFrame(other)
+                if (self.columns.get_indexer(other.columns) >= 0).all():
+                    other = other.reindex(columns=self.columns)
 
         from pandas.core.reshape.concat import concat
 

pandas/tests/frame/test_combine_concat.py

@@ -128,6 +128,20 @@ def test_concat_tuple_keys(self):
         )
         tm.assert_frame_equal(results, expected)
 
+    def test_append_empty_list(self):
+        # GH 28769
+        df = DataFrame()
+        result = df.append([])
+        expected = df
+        tm.assert_frame_equal(result, expected)
+        assert result is not df
+
+        df = DataFrame(np.random.randn(5, 4), columns=["foo", "bar", "baz", "qux"])
+        result = df.append([])
+        expected = df
+        tm.assert_frame_equal(result, expected)
+        assert result is not df  # .append() should return a new object
+
     def test_append_series_dict(self):
         df = DataFrame(np.random.randn(5, 4), columns=["foo", "bar", "baz", "qux"])