path reducer

flatten_dict/flatten_dict.py

@@ -2,11 +2,12 @@
 
 import six
 
-from .reducer import tuple_reducer
+from .reducer import tuple_reducer, path_reducer
 
 
 REDUCER_DICT = {
     'tuple': tuple_reducer,
+    'path': path_reducer,
 }
 
 def flatten(d, reducer='tuple', inverse=False):

flatten_dict/reducer.py

@@ -3,3 +3,10 @@ def tuple_reducer(k1, k2):
         return (k2,)
     else:
         return k1 + (k2,)
+
+def path_reducer(k1, k2):
+    import os.path
+    if k1 is None:
+        return k2
+    else:
+        return os.path.join(k1, k2)

flatten_dict/tests.py

@@ -38,3 +38,8 @@ def test_flatten_dict_inverse():
 
 def test_flatten_dict_with_reducer():
     assert flatten(normal_dict, reducer=tuple_reducer) == flat_normal_dict
+
+def test_flatten_dict_path():
+    from os.path import join
+    flat_path_dict = {join(*k): v for k, v in six.viewitems(flat_normal_dict)}
+    assert flatten(normal_dict, reducer='path') == flat_path_dict