Added utils.evaluate_vars function

netjsonconfig/utils.py

@@ -1,6 +1,9 @@
+import re
 from collections import OrderedDict
 from copy import deepcopy
 
+import six
+
 
 def merge_config(template, config):
     """
@@ -34,6 +37,32 @@ def sorted_dict(dictionary):
     return OrderedDict(sorted(dictionary.items()))
 
 
+var_pattern = re.compile(r'\{\{\s(\w*)\s\}\}')
+
+
+def evaluate_vars(data, context={}):
+    """
+    Evaluates variables in ``data``
+
+    :param data: data structure containing variables, may be
+                 ``str``, ``dict`` or ``list``
+    :param context: ``dict`` containing variables
+    :returns: modified data structure
+    """
+    if isinstance(data, (dict, list)):
+        if isinstance(data, dict):
+            loop_items = data.items()
+        elif isinstance(data, list):
+            loop_items = enumerate(data)
+        for key, value in loop_items:
+            data[key] = evaluate_vars(value, context)
+    elif isinstance(data, six.string_types):
+        for var in var_pattern.findall(data):
+            if var in context:
+                data = data.replace('{{ %s }}' % var, context[var])
+    return data
+
+
 class _TabsMixin(object):  # pragma: nocover
     """
     mixin that adds _tabs method to test classes

tests/test_utils.py

@@ -1,6 +1,6 @@
 import unittest
 
-from netjsonconfig.utils import merge_config
+from netjsonconfig.utils import evaluate_vars, merge_config
 
 
 class TestUtils(unittest.TestCase):
@@ -109,3 +109,27 @@ def test_merge_list_of_dicts_unchanged(self):
                 {"c": "original"}
             ]
         })
+
+    def test_evaluate_vars(self):
+        self.assertEqual(evaluate_vars('{{ tz }}', {'tz': 'UTC'}), 'UTC')
+        self.assertEqual(evaluate_vars('tz: {{ tz }}', {'tz': 'UTC'}), 'tz: UTC')
+
+    def test_evaluate_vars_missing(self):
+        self.assertEqual(evaluate_vars('{{ tz }}'), '{{ tz }}')
+        self.assertEqual(evaluate_vars('tz: {{ tz }}'), 'tz: {{ tz }}')
+
+    def test_evaluate_vars_dict(self):
+        val = evaluate_vars({'timezone': '{{ tz }}'}, {'tz': 'UTC'})
+        self.assertEqual(val, {'timezone': 'UTC'})
+
+    def test_evaluate_vars_nested_dict(self):
+        val = evaluate_vars({'general': {'timezone': '{{ tz }}'}}, {'tz': 'UTC'})
+        self.assertEqual(val, {'general': {'timezone': 'UTC'}})
+
+    def test_evaluate_vars_list(self):
+        val = evaluate_vars(['{{ a }}', '{{ b }}'], {'a': '1', 'b': '2'})
+        self.assertEqual(val, ['1', '2'])
+
+    def test_evaluate_vars_list_in_dict(self):
+        val = evaluate_vars({'l': ['{{ a }}', '{{ b }}']}, {'a': '1', 'b': '2'})
+        self.assertEqual(val, {'l': ['1', '2']})