feat(flags): Add support for variant overrides (#77)

CHANGELOG.md

@@ -1,3 +1,9 @@
+## 2.2.0 - 2022-11-14
+
+Changes:
+
+1. Add support for feature flag variant overrides with local evaluation
+
 ## 2.1.2 - 2022-09-15
 
 Changes:

README.md

@@ -39,7 +39,7 @@ Then navigate to `http://127.0.0.1:8080/sentry-debug/` and you should get an eve
 
 ### Releasing Versions
 
-Updated are released using GitHub Actions: after bumping `version.py` in `master`, go to [our release workflow's page](https://github.com/PostHog/posthog-python/actions/workflows/release.yaml) and dispatch it manually, using workflow from `master`.
+Updated are released using GitHub Actions: after bumping `version.py` in `master` and adding to `CHANGELOG.md`, go to [our release workflow's page](https://github.com/PostHog/posthog-python/actions/workflows/release.yaml) and dispatch it manually, using workflow from `master`.
 
 ## Questions?
 

example.py

@@ -8,14 +8,30 @@ import posthog
 posthog.debug = True
 
 # You can find this key on the /setup page in PostHog
-posthog.project_api_key = ""
-posthog.personal_api_key = ""
+posthog.project_api_key = "phc_gtWmTq3Pgl06u4sZY3TRcoQfp42yfuXHKoe8ZVSR6Kh"
+posthog.personal_api_key = "phx_fiRCOQkTA3o2ePSdLrFDAILLHjMu2Mv52vUi8MNruIm"
 
 # Where you host PostHog, with no trailing /.
 # You can remove this line if you're using posthog.com
 posthog.host = "http://localhost:8000"
 posthog.poll_interval = 10
 
+print(
+    posthog.feature_enabled(
+        "person-on-events-enabled",
+        "12345",
+        groups={"organization": str("0182ee91-8ef7-0000-4cb9-fedc5f00926a")},
+        group_properties={
+            "organization": {
+                "id": "0182ee91-8ef7-0000-4cb9-fedc5f00926a",
+                "created_at": "2022-06-30 11:44:52.984121+00:00",
+            }
+        },
+        only_evaluate_locally=True,
+    )
+)
+
+exit()
 
 # Capture an event
 posthog.capture("distinct_id", "event", {"property1": "value", "property2": "value"}, send_feature_flags=True)

posthog/feature_flags.py

@@ -46,12 +46,26 @@ def match_feature_flag_properties(flag, distinct_id, properties):
     flag_conditions = (flag.get("filters") or {}).get("groups") or []
     is_inconclusive = False
 
-    for condition in flag_conditions:
+    # Stable sort conditions with variant overrides to the top. This ensures that if overrides are present, they are
+    # evaluated first, and the variant override is applied to the first matching condition.
+    sorted_flag_conditions = sorted(
+        flag_conditions,
+        key=lambda condition: 0 if condition.get("variant") else 1,
+    )
+
+    for condition in sorted_flag_conditions:
         try:
             # if any one condition resolves to True, we can shortcircuit and return
             # the matching variant
             if is_condition_match(flag, distinct_id, condition, properties):
-                return get_matching_variant(flag, distinct_id) or True
+                variant_override = condition.get("variant")
+                # Some filters can be explicitly set to null, which require accessing variants like so
+                flag_variants = ((flag.get("filters") or {}).get("multivariate") or {}).get("variants") or []
+                if variant_override and variant_override in [variant["key"] for variant in flag_variants]:
+                    variant = variant_override
+                else:
+                    variant = get_matching_variant(flag, distinct_id)
+                return variant or True
         except InconclusiveMatchError:
             is_inconclusive = True
 

posthog/test/test_feature_flags.py

@@ -969,6 +969,186 @@ class TestLocalEvaluation(unittest.TestCase):
 
         self.assertFalse(client.feature_enabled("doesnt-exist", "distinct_id"))
 
+    @mock.patch("posthog.client.decide")
+    def test_get_feature_flag_with_variant_overrides(self, patch_decide):
+        patch_decide.return_value = {"featureFlags": {"beta-feature": "variant-1"}}
+        client = Client(FAKE_TEST_API_KEY, personal_api_key="test")
+        client.feature_flags = [
+            {
+                "id": 1,
+                "name": "Beta Feature",
+                "key": "beta-feature",
+                "is_simple_flag": False,
+                "active": True,
+                "rollout_percentage": 100,
+                "filters": {
+                    "groups": [
+                        {
+                            "properties": [
+                                {"key": "email", "type": "person", "value": "test@posthog.com", "operator": "exact"}
+                            ],
+                            "rollout_percentage": 100,
+                            "variant": "second-variant",
+                        },
+                        {"rollout_percentage": 50, "variant": "first-variant"},
+                    ],
+                    "multivariate": {
+                        "variants": [
+                            {"key": "first-variant", "name": "First Variant", "rollout_percentage": 50},
+                            {"key": "second-variant", "name": "Second Variant", "rollout_percentage": 25},
+                            {"key": "third-variant", "name": "Third Variant", "rollout_percentage": 25},
+                        ]
+                    },
+                },
+            }
+        ]
+        self.assertEqual(
+            client.get_feature_flag("beta-feature", "test_id", person_properties={"email": "test@posthog.com"}),
+            "second-variant",
+        )
+        self.assertEqual(client.get_feature_flag("beta-feature", "example_id"), "first-variant")
+        # decide not called because this can be evaluated locally
+        self.assertEqual(patch_decide.call_count, 0)
+
+    @mock.patch("posthog.client.decide")
+    def test_flag_with_clashing_variant_overrides(self, patch_decide):
+        patch_decide.return_value = {"featureFlags": {"beta-feature": "variant-1"}}
+        client = Client(FAKE_TEST_API_KEY, personal_api_key="test")
+        client.feature_flags = [
+            {
+                "id": 1,
+                "name": "Beta Feature",
+                "key": "beta-feature",
+                "is_simple_flag": False,
+                "active": True,
+                "rollout_percentage": 100,
+                "filters": {
+                    "groups": [
+                        {
+                            "properties": [
+                                {"key": "email", "type": "person", "value": "test@posthog.com", "operator": "exact"}
+                            ],
+                            "rollout_percentage": 100,
+                            "variant": "second-variant",
+                        },
+                        # since second-variant comes first in the list, it will be the one that gets picked
+                        {
+                            "properties": [
+                                {"key": "email", "type": "person", "value": "test@posthog.com", "operator": "exact"}
+                            ],
+                            "rollout_percentage": 100,
+                            "variant": "first-variant",
+                        },
+                        {"rollout_percentage": 50, "variant": "first-variant"},
+                    ],
+                    "multivariate": {
+                        "variants": [
+                            {"key": "first-variant", "name": "First Variant", "rollout_percentage": 50},
+                            {"key": "second-variant", "name": "Second Variant", "rollout_percentage": 25},
+                            {"key": "third-variant", "name": "Third Variant", "rollout_percentage": 25},
+                        ]
+                    },
+                },
+            }
+        ]
+        self.assertEqual(
+            client.get_feature_flag("beta-feature", "test_id", person_properties={"email": "test@posthog.com"}),
+            "second-variant",
+        )
+        self.assertEqual(
+            client.get_feature_flag("beta-feature", "example_id", person_properties={"email": "test@posthog.com"}),
+            "second-variant",
+        )
+        # decide not called because this can be evaluated locally
+        self.assertEqual(patch_decide.call_count, 0)
+
+    @mock.patch("posthog.client.decide")
+    def test_flag_with_invalid_variant_overrides(self, patch_decide):
+        patch_decide.return_value = {"featureFlags": {"beta-feature": "variant-1"}}
+        client = Client(FAKE_TEST_API_KEY, personal_api_key="test")
+        client.feature_flags = [
+            {
+                "id": 1,
+                "name": "Beta Feature",
+                "key": "beta-feature",
+                "is_simple_flag": False,
+                "active": True,
+                "rollout_percentage": 100,
+                "filters": {
+                    "groups": [
+                        {
+                            "properties": [
+                                {"key": "email", "type": "person", "value": "test@posthog.com", "operator": "exact"}
+                            ],
+                            "rollout_percentage": 100,
+                            "variant": "second???",
+                        },
+                        {"rollout_percentage": 50, "variant": "first??"},
+                    ],
+                    "multivariate": {
+                        "variants": [
+                            {"key": "first-variant", "name": "First Variant", "rollout_percentage": 50},
+                            {"key": "second-variant", "name": "Second Variant", "rollout_percentage": 25},
+                            {"key": "third-variant", "name": "Third Variant", "rollout_percentage": 25},
+                        ]
+                    },
+                },
+            }
+        ]
+        self.assertEqual(
+            client.get_feature_flag("beta-feature", "test_id", person_properties={"email": "test@posthog.com"}),
+            "third-variant",
+        )
+        self.assertEqual(client.get_feature_flag("beta-feature", "example_id"), "second-variant")
+        # decide not called because this can be evaluated locally
+        self.assertEqual(patch_decide.call_count, 0)
+
+    @mock.patch("posthog.client.decide")
+    def test_flag_with_multiple_variant_overrides(self, patch_decide):
+        patch_decide.return_value = {"featureFlags": {"beta-feature": "variant-1"}}
+        client = Client(FAKE_TEST_API_KEY, personal_api_key="test")
+        client.feature_flags = [
+            {
+                "id": 1,
+                "name": "Beta Feature",
+                "key": "beta-feature",
+                "is_simple_flag": False,
+                "active": True,
+                "rollout_percentage": 100,
+                "filters": {
+                    "groups": [
+                        {
+                            "rollout_percentage": 100,
+                            # The override applies even if the first condition matches all and gives everyone their default group
+                        },
+                        {
+                            "properties": [
+                                {"key": "email", "type": "person", "value": "test@posthog.com", "operator": "exact"}
+                            ],
+                            "rollout_percentage": 100,
+                            "variant": "second-variant",
+                        },
+                        {"rollout_percentage": 50, "variant": "third-variant"},
+                    ],
+                    "multivariate": {
+                        "variants": [
+                            {"key": "first-variant", "name": "First Variant", "rollout_percentage": 50},
+                            {"key": "second-variant", "name": "Second Variant", "rollout_percentage": 25},
+                            {"key": "third-variant", "name": "Third Variant", "rollout_percentage": 25},
+                        ]
+                    },
+                },
+            }
+        ]
+        self.assertEqual(
+            client.get_feature_flag("beta-feature", "test_id", person_properties={"email": "test@posthog.com"}),
+            "second-variant",
+        )
+        self.assertEqual(client.get_feature_flag("beta-feature", "example_id"), "third-variant")
+        self.assertEqual(client.get_feature_flag("beta-feature", "another_id"), "second-variant")
+        # decide not called because this can be evaluated locally
+        self.assertEqual(patch_decide.call_count, 0)
+
 
 class TestMatchProperties(unittest.TestCase):
     def property(self, key, value, operator=None):

posthog/version.py

@@ -1,4 +1,4 @@
-VERSION = "2.1.2"
+VERSION = "2.2.0"
 
 if __name__ == "__main__":
     print(VERSION, end="")