REF: use inheritance to concatenate categorical Indexes

Author: toobaz

pandas/core/indexes/base.py

@@ -1741,10 +1741,9 @@ def append(self, other):
         names = set([obj.name for obj in to_concat])
         name = None if len(names) > 1 else self.name
 
-        if self.is_categorical():
-            # if calling index is category, don't check dtype of others
-            from pandas.core.indexes.category import CategoricalIndex
-            return CategoricalIndex._append_same_dtype(self, to_concat, name)
+        return self._concat(to_concat, name)
+
+    def _concat(self, to_concat, name):
 
         typs = _concat.get_dtype_kinds(to_concat)
 

pandas/core/indexes/category.py

@@ -633,6 +633,10 @@ def insert(self, loc, item):
         codes = np.concatenate((codes[:loc], code, codes[loc:]))
         return self._create_from_codes(codes)
 
+    def _concat(self, to_concat, name):
+        # if calling index is category, don't check dtype of others
+        return CategoricalIndex._append_same_dtype(self, to_concat, name)
+
     def _append_same_dtype(self, to_concat, name):
         """
         Concatenate to_concat which has the same class