prepare 6.4.0 release (#95)

Author: eli-darkly

CHANGELOG.md

@@ -2,6 +2,13 @@
 
 All notable changes to the LaunchDarkly Python SDK will be documented in this file. This project adheres to [Semantic Versioning](http://semver.org).
 
+## [6.4.0] - 2018-08-29
+### Added:
+- The new `LDClient` method `variation_detail` allows you to evaluate a feature flag (using the same parameters as you would for `variation`) and receive more information about how the value was calculated. This information is returned in an `EvaluationDetail` object, which contains both the result value and a "reason" object which will tell you, for instance, if the user was individually targeted for the flag or was matched by one of the flag's rules, or if the flag returned the default value due to an error.
+
+### Fixed:
+- When evaluating a prerequisite feature flag, the analytics event for the evaluation did not include the result value if the prerequisite flag was off.
+
 ## [6.3.0] - 2018-08-27
 ### Added:
 - The new `LDClient` method `all_flags_state()` should be used instead of `all_flags()` if you are passing flag data to the front end for use with the JavaScript SDK. It preserves some flag metadata that the front end requires in order to send analytics events correctly. Versions 2.5.0 and above of the JavaScript SDK are able to use this metadata, but the output of `all_flags_state()` will still work with older versions.

ldclient/client.py

@@ -3,13 +3,14 @@
 import hashlib
 import hmac
 import threading
+import traceback
 
 from builtins import object
 
 from ldclient.config import Config as Config
 from ldclient.event_processor import NullEventProcessor
 from ldclient.feature_requester import FeatureRequesterImpl
-from ldclient.flag import evaluate
+from ldclient.flag import EvaluationDetail, evaluate, error_reason
 from ldclient.flags_state import FeatureFlagsState
 from ldclient.polling import PollingUpdateProcessor
 from ldclient.streaming import StreamingUpdateProcessor
@@ -184,69 +185,91 @@ def variation(self, key, user, default):
           available from LaunchDarkly
         :return: one of the flag's variation values, or the default value
         """
+        return self._evaluate_internal(key, user, default, False).value
+    
+    def variation_detail(self, key, user, default):
+        """Determines the variation of a feature flag for a user, like `variation`, but also
+        provides additional information about how this value was calculated.
+        
+        The return value is an EvaluationDetail object, which has three properties:
+
+        `value`: the value that was calculated for this user (same as the return value
+        of `variation`)
+        
+        `variation_index`: the positional index of this value in the flag, e.g. 0 for the
+        first variation - or `None` if the default value was returned
+        
+        `reason`: a hash describing the main reason why this value was selected.
+        
+        The `reason` will also be included in analytics events, if you are capturing
+        detailed event data for this flag.
+        
+        :param string key: the unique key for the feature flag
+        :param dict user: a dictionary containing parameters for the end user requesting the flag
+        :param object default: the default value of the flag, to be used if the value is not
+          available from LaunchDarkly
+        :return: an EvaluationDetail object describing the result
+        :rtype: EvaluationDetail
+        """
+        return self._evaluate_internal(key, user, default, True)
+    
+    def _evaluate_internal(self, key, user, default, include_reasons_in_events):
         default = self._config.get_default(key, default)
-        if user is not None:
-            self._sanitize_user(user)
 
         if self._config.offline:
-            return default
+            return EvaluationDetail(default, None, error_reason('CLIENT_NOT_READY'))
+        
+        if user is not None:
+            self._sanitize_user(user)
 
-        def send_event(value, version=None):
-            self._send_event({'kind': 'feature', 'key': key, 'user': user, 'variation': None,
-                              'value': value, 'default': default, 'version': version,
-                              'trackEvents': False, 'debugEventsUntilDate': None})
+        def send_event(value, variation=None, flag=None, reason=None):
+            self._send_event({'kind': 'feature', 'key': key, 'user': user,
+                              'value': value, 'variation': variation, 'default': default,
+                              'version': flag.get('version') if flag else None,
+                              'trackEvents': flag.get('trackEvents') if flag else None,
+                              'debugEventsUntilDate': flag.get('debugEventsUntilDate') if flag else None,
+                              'reason': reason if include_reasons_in_events else None})
 
         if not self.is_initialized():
             if self._store.initialized:
                 log.warn("Feature Flag evaluation attempted before client has initialized - using last known values from feature store for feature key: " + key)
             else:
                 log.warn("Feature Flag evaluation attempted before client has initialized! Feature store unavailable - returning default: "
                          + str(default) + " for feature key: " + key)
-                send_event(default)
-                return default
-
+                reason = error_reason('CLIENT_NOT_READY')
+                send_event(default, None, None, reason)
+                return EvaluationDetail(default, None, reason)
+        
         if user is not None and user.get('key', "") == "":
             log.warn("User key is blank. Flag evaluation will proceed, but the user will not be stored in LaunchDarkly.")
 
-        def cb(flag):
-            try:
-                if not flag:
-                    log.info("Feature Flag key: " + key + " not found in Feature Store. Returning default.")
-                    send_event(default)
-                    return default
-
-                return self._evaluate_and_send_events(flag, user, default)
-
-            except Exception as e:
-                log.error("Exception caught in variation: " + e.message + " for flag key: " + key + " and user: " + str(user))
-                send_event(default)
-
-            return default
-
-        return self._store.get(FEATURES, key, cb)
-
-    def _evaluate(self, flag, user):
-        return evaluate(flag, user, self._store)
-
-    def _evaluate_and_send_events(self, flag, user, default):
-        if user is None or user.get('key') is None:
-            log.warn("Missing user or user key when evaluating Feature Flag key: " + flag.get('key') + ". Returning default.")
-            value = default
-            variation = None
+        flag = self._store.get(FEATURES, key, lambda x: x)
+        if not flag:
+            reason = error_reason('FLAG_NOT_FOUND')
+            send_event(default, None, None, reason)
+            return EvaluationDetail(default, None, reason)
         else:
-            result = evaluate(flag, user, self._store)
-            for event in result.events or []:
-                self._send_event(event)
-            value = default if result.value is None else result.value
-            variation = result.variation
-        
-        self._send_event({'kind': 'feature', 'key': flag.get('key'),
-                          'user': user, 'variation': variation, 'value': value,
-                          'default': default, 'version': flag.get('version'),
-                          'trackEvents': flag.get('trackEvents'),
-                          'debugEventsUntilDate': flag.get('debugEventsUntilDate')})
-        return value
+            if user is None or user.get('key') is None:
+                reason = error_reason('USER_NOT_SPECIFIED')
+                send_event(default, None, flag, reason)
+                return EvaluationDetail(default, None, reason)
 
+            try:
+                result = evaluate(flag, user, self._store, include_reasons_in_events)
+                for event in result.events or []:
+                    self._send_event(event)
+                detail = result.detail
+                if detail.is_default_value():
+                    detail = EvaluationDetail(default, None, detail.reason)
+                send_event(detail.value, detail.variation_index, flag, detail.reason)
+                return detail
+            except Exception as e:
+                log.error("Unexpected error while evaluating feature flag \"%s\": %s" % (key, e))
+                log.debug(traceback.format_exc())
+                reason = error_reason('EXCEPTION')
+                send_event(default, None, flag, reason)
+                return EvaluationDetail(default, None, reason)
+    
     def all_flags(self, user):
         """Returns all feature flag values for the given user.
         
@@ -272,7 +295,8 @@ def all_flags_state(self, user, **kwargs):
         :param dict user: the end user requesting the feature flags
         :param kwargs: optional parameters affecting how the state is computed: set
           `client_side_only=True` to limit it to only flags that are marked for use with the
-          client-side SDK (by default, all flags are included)
+          client-side SDK (by default, all flags are included); set `with_reasons=True` to
+          include evaluation reasons in the state (see `variation_detail`)
         :return: a FeatureFlagsState object (will never be None; its 'valid' property will be False
           if the client is offline, has not been initialized, or the user is None or has no key)
         :rtype: FeatureFlagsState
@@ -294,6 +318,7 @@ def all_flags_state(self, user, **kwargs):
 
         state = FeatureFlagsState(True)
         client_only = kwargs.get('client_side_only', False)
+        with_reasons = kwargs.get('with_reasons', False)
         try:
             flags_map = self._store.all(FEATURES, lambda x: x)
         except Exception as e:
@@ -304,11 +329,14 @@ def all_flags_state(self, user, **kwargs):
             if client_only and not flag.get('clientSide', False):
                 continue
             try:
-                result = self._evaluate(flag, user)
-                state.add_flag(flag, result.value, result.variation)
+                detail = evaluate(flag, user, self._store, False).detail
+                state.add_flag(flag, detail.value, detail.variation_index,
+                    detail.reason if with_reasons else None)
             except Exception as e:
                 log.error("Error evaluating flag \"%s\" in all_flags_state: %s" % (key, e))
-                state.add_flag(flag, None, None)
+                log.debug(traceback.format_exc())
+                reason = {'kind': 'ERROR', 'errorKind': 'EXCEPTION'}
+                state.add_flag(flag, None, None, reason if with_reasons else None)
 
         return state
 

ldclient/event_processor.py

@@ -84,6 +84,8 @@ def make_output_event(self, e):
                 out['user'] = self._user_filter.filter_user_props(e['user'])
             else:
                 out['userKey'] = e['user'].get('key')
+            if e.get('reason'):
+                out['reason'] = e.get('reason')
             return out
         elif kind == 'identify':
             return {