feat(feature-flags): support quota limiting for feature flags (#195)

* haha okay

* tests workin

* format

* use case-sensitive comparisons

* omg LOL

* fix tests

* jeez

* this will probably work

* now do local eval

* okay

* yo

* formatting

* fix import order

* type check

* ai yi yi

* code review

* format

Author: dmarticus

CHANGELOG.md

@@ -1,3 +1,7 @@
+## 3.15.0 - 2025-02-19
+
+1. Support quota-limited feature flags
+
 ## 3.14.2 - 2025-02-19
 
 1. Evaluate feature flag payloads with case sensitivity correctly.  Fixes <https://github.com/PostHog/posthog-python/issues/178>

posthog/client.py

@@ -600,6 +600,19 @@ def _load_feature_flags(self):
                         "To use feature flags, please set a personal_api_key "
                         "More information: https://posthog.com/docs/api/overview",
                     )
+            elif e.status == 402:
+                self.log.warning("[FEATURE FLAGS] PostHog feature flags quota limited")
+                # Reset all feature flag data when quota limited
+                self.feature_flags = []
+                self.feature_flags_by_key = {}
+                self.group_type_mapping = {}
+                self.cohorts = {}
+
+                if self.debug:
+                    raise APIError(
+                        status=402,
+                        message="PostHog feature flags quota limited",
+                    )
             else:
                 self.log.error(f"[FEATURE FLAGS] Error loading feature flags: {e}")
         except Exception as e:

posthog/request.py

@@ -68,7 +68,19 @@ def _process_response(
     log = logging.getLogger("posthog")
     if res.status_code == 200:
         log.debug(success_message)
-        return res.json() if return_json else res
+        response = res.json() if return_json else res
+        # Handle quota limited decide responses by raising a specific error
+        # NB: other services also put entries into the quotaLimited key, but right now we only care about feature flags
+        # since most of the other services handle quota limiting in other places in the application.
+        if (
+            isinstance(response, dict)
+            and "quotaLimited" in response
+            and isinstance(response["quotaLimited"], list)
+            and "feature_flags" in response["quotaLimited"]
+        ):
+            log.warning("PostHog feature flags quota limited")
+            raise QuotaLimitError(res.status_code, "Feature flags quota limited")
+        return response
     try:
         payload = res.json()
         log.debug("received response: %s", payload)
@@ -112,6 +124,10 @@ def __str__(self):
         return msg.format(self.message, self.status)
 
 
+class QuotaLimitError(APIError):
+    pass
+
+
 class DatetimeSerializer(json.JSONEncoder):
     def default(self, obj: Any):
         if isinstance(obj, (date, datetime)):

posthog/test/test_client.py

@@ -7,6 +7,7 @@
 import six
 
 from posthog.client import Client
+from posthog.request import APIError
 from posthog.test.test_utils import FAKE_TEST_API_KEY
 from posthog.version import VERSION
 
@@ -384,6 +385,25 @@ def test_basic_capture_with_locally_evaluated_feature_flags(self, patch_decide):
         assert "$feature/false-flag" not in msg["properties"]
         assert "$active_feature_flags" not in msg["properties"]
 
+    @mock.patch("posthog.client.get")
+    def test_load_feature_flags_quota_limited(self, patch_get):
+        mock_response = {
+            "type": "quota_limited",
+            "detail": "You have exceeded your feature flag request quota",
+            "code": "payment_required",
+        }
+        patch_get.side_effect = APIError(402, mock_response["detail"])
+
+        client = Client(FAKE_TEST_API_KEY, personal_api_key="test")
+        with self.assertLogs("posthog", level="WARNING") as logs:
+            client._load_feature_flags()
+
+            self.assertEqual(client.feature_flags, [])
+            self.assertEqual(client.feature_flags_by_key, {})
+            self.assertEqual(client.group_type_mapping, {})
+            self.assertEqual(client.cohorts, {})
+            self.assertIn("PostHog feature flags quota limited", logs.output[0])
+
     @mock.patch("posthog.client.decide")
     def test_dont_override_capture_with_local_flags(self, patch_decide):
         patch_decide.return_value = {"featureFlags": {"beta-feature": "random-variant"}}

posthog/test/test_request.py

@@ -2,10 +2,11 @@
 import unittest
 from datetime import date, datetime
 
+import mock
 import pytest
 import requests
 
-from posthog.request import DatetimeSerializer, batch_post, determine_server_host
+from posthog.request import DatetimeSerializer, QuotaLimitError, batch_post, decide, determine_server_host
 from posthog.test.test_utils import TEST_API_KEY
 
 
@@ -44,6 +45,36 @@ def test_should_timeout(self):
                 "key", batch=[{"distinct_id": "distinct_id", "event": "python event", "type": "track"}], timeout=0.0001
             )
 
+    def test_quota_limited_response(self):
+        mock_response = requests.Response()
+        mock_response.status_code = 200
+        mock_response._content = json.dumps(
+            {
+                "quotaLimited": ["feature_flags"],
+                "featureFlags": {},
+                "featureFlagPayloads": {},
+                "errorsWhileComputingFlags": False,
+            }
+        ).encode("utf-8")
+
+        with mock.patch("posthog.request._session.post", return_value=mock_response):
+            with self.assertRaises(QuotaLimitError) as cm:
+                decide("fake_key", "fake_host")
+
+            self.assertEqual(cm.exception.status, 200)
+            self.assertEqual(cm.exception.message, "Feature flags quota limited")
+
+    def test_normal_decide_response(self):
+        mock_response = requests.Response()
+        mock_response.status_code = 200
+        mock_response._content = json.dumps(
+            {"featureFlags": {"flag1": True}, "featureFlagPayloads": {}, "errorsWhileComputingFlags": False}
+        ).encode("utf-8")
+
+        with mock.patch("posthog.request._session.post", return_value=mock_response):
+            response = decide("fake_key", "fake_host")
+            self.assertEqual(response["featureFlags"], {"flag1": True})
+
 
 @pytest.mark.parametrize(
     "host, expected",

posthog/version.py

@@ -1,4 +1,4 @@
-VERSION = "3.14.2"
+VERSION = "3.15.0"
 
 if __name__ == "__main__":
     print(VERSION, end="")  # noqa: T201