[general] Avoid default mutable arguments

netjsonconfig/backends/base/backend.py

@@ -21,8 +21,9 @@ class BaseBackend(object):
     schema = None
     FILE_SECTION_DELIMITER = '# ---------- files ---------- #'
     intermediate_data = None
+    list_identifiers = []
 
-    def __init__(self, config, templates=[], context={}):
+    def __init__(self, config, templates=None, context=None):
         """
         :param config: ``dict`` containing valid **NetJSON DeviceConfiguration**
         :param templates: ``list`` containing **NetJSON** dictionaries that will be
@@ -54,17 +55,17 @@ def _merge_config(self, config, templates):
         """
         Merges config with templates
         """
+        if not templates:
+            return config
         # type check
         if not isinstance(templates, list):
             raise TypeError('templates argument must be an instance of list')
-        # merge any present template with main configuration
+        # merge templates with main configuration
         base_config = {}
-
         for template in templates:
-            template = self._load(template)
-            base_config = merge_config(base_config, template)
+            base_config = merge_config(base_config, self._load(template), self.list_identifiers)
         if base_config:
-            return merge_config(base_config, config)
+            return merge_config(base_config, config, self.list_identifiers)
         return config
 
     def _evaluate_vars(self, config, context):

netjsonconfig/backends/openwisp/openwisp.py

@@ -25,10 +25,11 @@ def _sanitize_radios(self):
         for radio in self.config.get('radios', []):
             radio.setdefault('disabled', False)
 
-    def _render_template(self, template, context={}):
+    def _render_template(self, template, context=None):
         openwisp_env = Environment(loader=PackageLoader(self.__module__, 'templates'),
                                    trim_blocks=True)
         template = openwisp_env.get_template(template)
+        context = context or {}
         return template.render(**context)
 
     def _add_unique_file(self, item):

netjsonconfig/backends/openwrt/openwrt.py

@@ -28,6 +28,7 @@ class OpenWrt(BaseBackend):
         converters.Default,
     ]
     renderer = OpenWrtRenderer
+    list_identifiers = ['name', 'config_value', 'id']
 
     def _generate_contents(self, tar):
         """

netjsonconfig/utils.py

@@ -5,7 +5,7 @@
 import six
 
 
-def merge_config(template, config):
+def merge_config(template, config, list_identifiers=None):
     """
     Merges ``config`` on top of ``template``.
 
@@ -19,6 +19,7 @@ def merge_config(template, config):
 
     :param template: template ``dict``
     :param config: config ``dict``
+    :param list_identifiers: ``list`` or ``None``
     :returns: merged ``dict``
     """
     result = template.copy()
@@ -27,13 +28,13 @@ def merge_config(template, config):
             node = result.get(key, {})
             result[key] = merge_config(node, value)
         elif isinstance(value, list) and isinstance(result.get(key), list):
-            result[key] = merge_list(result[key], value)
+            result[key] = merge_list(result[key], value, list_identifiers)
         else:
             result[key] = value
     return result
 
 
-def merge_list(list1, list2, identifiers=['name', 'config_value', 'id']):
+def merge_list(list1, list2, identifiers=None):
     """
     Merges ``list2`` on top of ``list1``.
 
@@ -43,10 +44,12 @@ def merge_list(list1, list2, identifiers=['name', 'config_value', 'id']):
     The remaining elements will be summed in order to create a list
     which contains elements of both lists.
 
-    :param list1: list from template
-    :param list2: list from config
+    :param list1: ``list`` from template
+    :param list2: ``list from config
+    :param identifiers: ``list`` or ``None``
     :returns: merged ``list``
     """
+    identifiers = identifiers or []
     dict_map = {'list1': OrderedDict(), 'list2': OrderedDict()}
     counter = 1
     for list_ in [list1, list2]:

tests/openwrt/test_backend.py

@@ -209,7 +209,7 @@ def test_templates_type_error(self):
             }
         }
         with self.assertRaises(TypeError):
-            OpenWrt(config, templates={})
+            OpenWrt(config, templates={'a': 'a'})
 
     def test_templates_config_error(self):
         config = {

tests/test_utils.py

@@ -173,7 +173,7 @@ def test_evaluate_vars_one_char(self):
     def test_merge_list_override(self):
         template = [{"name": "test1", "tx": 1}]
         config = [{"name": "test1", "tx": 2}]
-        result = merge_list(template, config)
+        result = merge_list(template, config, ['name'])
         self.assertEqual(result, config)
 
     def test_merge_list_union_and_override(self):
@@ -182,7 +182,7 @@ def test_merge_list_union_and_override(self):
             {"id": "test1", "a": "0", "b": "b"},
             {"id": "test2", "c": "c"}
         ]
-        result = merge_list(template, config)
+        result = merge_list(template, config, ['id'])
         self.assertEqual(result, [
             {"id": "test1", "a": "0", "b": "b"},
             {"id": "test2", "c": "c"}
@@ -191,7 +191,7 @@ def test_merge_list_union_and_override(self):
     def test_merge_list_config_value(self):
         template = [{"config_value": "test1", "tx": 1}]
         config = [{"config_value": "test1", "tx": 2}]
-        result = merge_list(template, config)
+        result = merge_list(template, config, ['config_value'])
         self.assertEqual(result, config)
 
     def test_get_copy_default(self):