merge_dict now returns a copy of all the elements #26

Data structures passed as parameters are not modified.

Closes #26

netjsonconfig/utils.py

@@ -1,23 +1,24 @@
 from collections import OrderedDict
+from copy import deepcopy
 
 
 def merge_config(template, config):
     """
     merge two dicts `template` and `config`
     values of `config` are merged in values present in `template`
     lists present in `config` will be added to lists in `template`
+    returns merged dict
     """
+    result = template.copy()
     for key, value in config.items():
         if isinstance(value, dict):
-            # get node or create one
-            node = template.setdefault(key, {})
-            merge_config(node, value)
-        elif isinstance(value, list) and isinstance(template.get(key), list):
-            template[key] += value
+            node = result.get(key, {})
+            result[key] = merge_config(node, value)
+        elif isinstance(value, list) and isinstance(result.get(key), list):
+            result[key] = deepcopy(result[key]) + deepcopy(value)
         else:
-            template[key] = value
-
-    return template
+            result[key] = value
+    return result
 
 
 def sorted_dict(dictionary):

tests/test_utils.py

@@ -48,3 +48,64 @@ def test_merge_config_list(self):
                 "element2"
             ]
         })
+
+    def test_merge_originals_unchanged(self):
+        template = {
+            "str": "original",
+            "dict": {"a": "a"},
+            "list": ["element1"]
+        }
+        config = {
+            "str": "changed",
+            "dict": {"b": "b"},
+            "list": ["element2"]
+        }
+        result = merge_config(template, config)
+        # ensure original structures not changed
+        self.assertEqual(template, {
+            "str": "original",
+            "dict": {"a": "a"},
+            "list": ["element1"]
+        })
+        self.assertEqual(config, {
+            "str": "changed",
+            "dict": {"b": "b"},
+            "list": ["element2"]
+        })
+
+    def test_merge_list_of_dicts_unchanged(self):
+        template = {
+            "list": [
+                {"a": "original"},
+                {"b": "original"}
+            ]
+        }
+        config = {
+            "list": [
+                {"c": "original"}
+            ]
+        }
+        result = merge_config(template, config)
+        template['list'][0]['a'] = 'changed'
+        config['list'][0]['c'] = 'changed'
+        result['list'][1]['b'] = 'changed'
+        # ensure originals changed
+        # but not result of merge
+        self.assertEqual(template, {
+            "list": [
+                {"a": "changed"},
+                {"b": "original"}
+            ]
+        })
+        self.assertEqual(config, {
+            "list": [
+                {"c": "changed"}
+            ]
+        })
+        self.assertEqual(result, {
+            "list": [
+                {"a": "original"},
+                {"b": "changed"},
+                {"c": "original"}
+            ]
+        })