BUG/API: Index.append with mixed object/Categorical indices (#14545)

* BUG/API: Index.append with mixed object/Categorical indices

* Only coerce to object if the calling index is not categorical

* Add test for the df.info() case (GH14298)

Author: jorisvandenbossche

pandas/indexes/base.py

@@ -1464,13 +1464,13 @@ def append(self, other):
         names = set([obj.name for obj in to_concat])
         name = None if len(names) > 1 else self.name
 
-        typs = _concat.get_dtype_kinds(to_concat)
-
-        if 'category' in typs:
-            # if any of the to_concat is category
+        if self.is_categorical():
+            # if calling index is category, don't check dtype of others
             from pandas.indexes.category import CategoricalIndex
             return CategoricalIndex._append_same_dtype(self, to_concat, name)
 
+        typs = _concat.get_dtype_kinds(to_concat)
+
         if len(typs) == 1:
             return self._append_same_dtype(to_concat, name=name)
         return _concat._concat_index_asobject(to_concat, name=name)

pandas/tests/frame/test_repr_info.py

@@ -405,3 +405,11 @@ def memory_usage(f):
 
         # high upper bound
         self.assertTrue(memory_usage(unstacked) - memory_usage(df) < 2000)
+
+    def test_info_categorical(self):
+        # GH14298
+        idx = pd.CategoricalIndex(['a', 'b'])
+        df = pd.DataFrame(np.zeros((2, 2)), index=idx, columns=idx)
+
+        buf = StringIO()
+        df.info(buf=buf)

pandas/tests/indexes/test_category.py

@@ -278,6 +278,11 @@ def test_append(self):
         # invalid objects
         self.assertRaises(TypeError, lambda: ci.append(Index(['a', 'd'])))
 
+        # GH14298 - if base object is not categorical -> coerce to object
+        result = Index(['c', 'a']).append(ci)
+        expected = Index(list('caaabbca'))
+        tm.assert_index_equal(result, expected, exact=True)
+
     def test_insert(self):
 
         ci = self.create_index()