Add Rules.from_dict classmethod

Many services currently construct a Rules instance from a dictionary in
their tests. It would be beneficial to them if they didn't have to
import oslo_policy._parser in order to parse a rule before passing it to
Rules.__init__. Adding a Rules.from_dict classmethod should satisfy the
need to create a Rules instance from a dictionary in tests.

Change-Id: I3d73059277c45d4852f842474c6f1d61daa349b8

2 files changed, 17 insertions, 0 deletions

diff --git a/oslo_policy/policy.py b/oslo_policy/policy.py
index 0f617f0..e4f4a07 100644
--- a/oslo_policy/policy.py
+++ b/oslo_policy/policy.py
@@ -240,6 +240,15 @@ class Rules(dict):
 
         return cls(rules, default_rule)
 
+    @classmethod
+    def from_dict(cls, rules_dict, default_rule=None):
+        """Allow loading of rule data from a dictionary."""
+
+        # Parse the rules stored in the dictionary
+        rules = dict((k, _parser.parse_rule(v)) for k, v in rules_dict.items())
+
+        return cls(rules, default_rule)
+
     def __init__(self, rules=None, default_rule=None):
         """Initialize the Rules store."""
 
diff --git a/oslo_policy/tests/test_policy.py b/oslo_policy/tests/test_policy.py
index 3d3fe9e..3401cb5 100644
--- a/oslo_policy/tests/test_policy.py
+++ b/oslo_policy/tests/test_policy.py
@@ -109,6 +109,14 @@ class RulesTestCase(test_base.BaseTestCase):
             default=[],
         ))
 
+    @mock.patch.object(_parser, 'parse_rule', lambda x: x)
+    def test_from_dict(self):
+        expected = {'admin_or_owner': 'role:admin', 'default': '@'}
+        rules = policy.Rules.from_dict(expected, 'default')
+
+        self.assertEqual('default', rules.default_rule)
+        self.assertEqual(expected, rules)
+
     def test_str(self):
         exemplar = """{
     "admin_or_owner": "role:admin or project_id:%(project_id)s"