REF: move _concat_indexes to pandas.core.dtypes.concat

Author: toobaz

pandas/core/dtypes/concat.py

@@ -491,3 +491,27 @@ def convert_sparse(x, axis):
         # coerce to object if needed
         result = result.astype('object')
     return result
+
+
+def _concat_indexes(to_concat):
+    """
+    Concatenate elements of to_concat to single Index
+
+    Parameters
+    ----------
+    to_concat : list-like of indexes
+
+    Returns
+    -------
+    a single index, preserving the combined dtypes
+    """
+
+    if len(to_concat) == 0:
+        from pandas.core.index import Index
+        return Index([])
+
+    typs = get_dtype_kinds(to_concat)
+    if len(typs) == 1:
+        return to_concat[0].__class__._concat_same_dtype(to_concat)
+    else:
+        return _concat_index_asobject(to_concat)

pandas/core/indexes/base.py

@@ -1686,15 +1686,11 @@ def append(self, other):
         return res
 
     @classmethod
-    def _concat(self, to_concat):
+    def _concat(cls, to_concat):
         """
         Concatenate to_concat to single Index
         """
-        typs = _concat.get_dtype_kinds(to_concat)
-        if len(typs) == 1:
-            return self._concat_same_dtype(to_concat)
-        else:
-            return _concat._concat_index_asobject(to_concat)
+        return _concat._concat_indexes(to_concat)
 
     @classmethod
     def _concat_same_dtype(cls, to_concat):