feat(flags): typed flag value accessors

.sampo/changesets/flags-typed-accessors.md

@@ -0,0 +1,5 @@
+---
+pypi/posthog: minor
+---
+
+Add `get_boolean_value`, `get_string_value`, `get_number_value`, `get_integer_value`, `get_float_value` and `get_object_value` to the `evaluate_flags()` result, each with a `_details` form that returns a `FlagEvaluationDetails` with an OpenFeature `reason`, `error_code` and `flag_metadata`. These accessors never coerce and never raise: they return your default when the flag is missing, failed, unreadable, has no value, or has a value of another type, and an object value too deeply nested to copy reads as unreadable. A read of a value of another type (`TYPE_MISMATCH`) is a bug in the calling code: it sends no `$feature_flag_called` and leaves the dedupe cache alone, but still counts as accessed for `only_accessed()`. The next read of the right type, or a `get_flag()` or `is_enabled()` read, reports the flag. The SDK logs the details' `error_message` as an error once per client for each flag and requested type. Numbers are IEEE-754 doubles: `get_number_value` returns an integer beyond `2**53 - 1` in magnitude as the nearest `float`, `get_float_value` returns every number as the nearest `float`, and both return an infinity for an integer beyond the range of a double, as JavaScript parses it. `get_integer_value` returns your default with `TYPE_MISMATCH` for an integer beyond `2**53 - 1`. Each accessor takes the keyword-only `send_feature_flag_events` option, like `is_enabled()` and `get_flag()`: pass `send_feature_flag_events=False` to read a flag without sending `$feature_flag_called`. The key still counts as accessed for `only_accessed()`, and a later read that sends events still reports the flag. Details of a locally evaluated flag have `config_version` 1 and carry the `id` and `version` of the local flag definition in `flag_metadata`. `FeatureFlag` gains `value` (the typed value), `failed`, and `error_code` and `error_message`, which say why a flag failed or could not be read. `FlagMetadata` gains `config_version`, `rule_type`, `rule_id`, `variant_key` and `forced_variant`. Number and object values need a server that sends typed values; the SDK logs once per client when it reads a response without them.

posthog/__init__.py

@@ -81,6 +81,9 @@
     BeforeSendCallback as BeforeSendCallback,
     FeatureFlag as FeatureFlag,
     FeatureFlagEvaluationRuntime as FeatureFlagEvaluationRuntime,
+    FlagEvaluationDetails as FlagEvaluationDetails,
+    FlagEvaluationErrorCode as FlagEvaluationErrorCode,
+    FlagEvaluationReason as FlagEvaluationReason,
     FlagValue as FlagValue,
     FlagsAndPayloads as FlagsAndPayloads,
     UnresolvedFlagReason as UnresolvedFlagReason,

posthog/async_client.py

@@ -237,6 +237,9 @@ def __init__(
             self.log.setLevel(logging.WARNING)
         # Whether this client has logged that /flags sent records without typed values.
         self._logged_untyped_flags_response = False
+        # The (flag key, requested type) pairs of typed reads of the wrong type that
+        # this client has logged. Same bound and eviction as the flag-event dedupe.
+        self._logged_flag_type_mismatches = SizeLimitedDict(_MAX_DICT_SIZE)
 
         if not self.api_key:
             self.log.error(
@@ -899,9 +902,18 @@ def _get_feature_flag_evaluations_host(self) -> _FeatureFlagEvaluationsHost:
             self._feature_flag_evaluations_host_cache = _FeatureFlagEvaluationsHost(
                 capture_flag_called_event_if_needed=self._capture_feature_flag_called_if_needed,
                 log_warning=lambda message: self.log.warning(message),
+                log_type_mismatch=self._log_flag_type_mismatch,
             )
         return self._feature_flag_evaluations_host_cache
 
+    def _log_flag_type_mismatch(self, key: str, value_type: str, message: str) -> None:
+        """Log a typed flag read of the wrong type, once per flag key and type."""
+        logged_key = (key, value_type)
+        if logged_key in self._logged_flag_type_mismatches:
+            return
+        self._logged_flag_type_mismatches[logged_key] = True
+        self.log.error(message)
+
     async def _get_flags_decision(
         self,
         distinct_id: ID_TYPES,

posthog/client.py

@@ -1022,6 +1022,9 @@ def __init__(
         self._minimal_flag_called_events: bool = False
         # Whether this client has logged that /flags sent records without typed values.
         self._logged_untyped_flags_response = False
+        # The (flag key, requested type) pairs of typed reads of the wrong type that
+        # this client has logged. Same bound and eviction as the flag-event dedupe.
+        self._logged_flag_type_mismatches = SizeLimitedDict(MAX_DICT_SIZE)
 
         self.capture_trace_context = capture_trace_context
         self.capture_exception_code_variables = capture_exception_code_variables
@@ -5020,6 +5023,7 @@ def evaluate_flags(
                 key=key,
                 enabled=value is not False,
                 variant=value if isinstance(value, str) else None,
+                inactive=value is False and not flag_def.get("active"),
                 payload=_parse_flag_payload(local_payloads.get(key)),
                 id=flag_def.get("id"),
                 version=flag_def.get("version"),
@@ -5091,9 +5095,18 @@ def _get_feature_flag_evaluations_host(self) -> _FeatureFlagEvaluationsHost:
             self._feature_flag_evaluations_host_cache = _FeatureFlagEvaluationsHost(
                 capture_flag_called_event_if_needed=self._capture_feature_flag_called_if_needed,
                 log_warning=lambda message: self.log.warning(message),
+                log_type_mismatch=self._log_flag_type_mismatch,
             )
         return self._feature_flag_evaluations_host_cache
 
+    def _log_flag_type_mismatch(self, key: str, value_type: str, message: str) -> None:
+        """Log a typed flag read of the wrong type, once per flag key and type."""
+        logged_key = (key, value_type)
+        if logged_key in self._logged_flag_type_mismatches:
+            return
+        self._logged_flag_type_mismatches[logged_key] = True
+        self.log.error(message)
+
     def _get_all_flags_and_payloads_locally(
         self,
         distinct_id: ID_TYPES,