feat: added variable evaluation hooks (#89)

* chore: revert local client changes

* feat: added variable evaluation hooks

* chore: added local client implementation for hooks

Author: jsalaber

devcycle_python_sdk/cloud_client.py

@@ -9,6 +9,13 @@
     NotFoundError,
     CloudClientUnauthorizedError,
 )
+from devcycle_python_sdk.managers.eval_hooks_manager import (
+    EvalHooksManager,
+    BeforeHookError,
+    AfterHookError,
+)
+from devcycle_python_sdk.models.eval_hook import EvalHook
+from devcycle_python_sdk.models.eval_hook_context import HookContext
 from devcycle_python_sdk.models.user import DevCycleUser
 from devcycle_python_sdk.models.event import DevCycleEvent
 from devcycle_python_sdk.models.variable import Variable
@@ -45,6 +52,9 @@ def __init__(self, sdk_key: str, options: DevCycleCloudOptions):
         self.sdk_type = "server"
         self.bucketing_api = BucketingAPIClient(sdk_key, self.options)
         self._openfeature_provider = DevCycleProvider(self)
+        self.eval_hooks_manager = EvalHooksManager(
+            None if options is None else options.eval_hooks
+        )
 
     def get_sdk_platform(self) -> str:
         return "Cloud"
@@ -87,8 +97,24 @@ def variable(self, user: DevCycleUser, key: str, default_value: Any) -> Variable
         if default_value is None:
             raise ValueError("Missing parameter: defaultValue")
 
+        context = HookContext(key, user, default_value)
+        variable = Variable.create_default_variable(
+            key=key, default_value=default_value
+        )
+
         try:
-            variable = self.bucketing_api.variable(key, user)
+            before_hook_error = None
+            try:
+                changed_context = self.eval_hooks_manager.run_before(context)
+                if changed_context is not None:
+                    context = changed_context
+            except BeforeHookError as e:
+                before_hook_error = e
+            variable = self.bucketing_api.variable(key, context.user)
+            if before_hook_error is None:
+                self.eval_hooks_manager.run_after(context, variable)
+            else:
+                raise before_hook_error
         except CloudClientUnauthorizedError as e:
             logger.warning("DevCycle: SDK key is invalid, unable to make cloud request")
             raise e
@@ -97,11 +123,17 @@ def variable(self, user: DevCycleUser, key: str, default_value: Any) -> Variable
             return Variable.create_default_variable(
                 key=key, default_value=default_value
             )
+        except BeforeHookError as e:
+            self.eval_hooks_manager.run_error(context, e)
+        except AfterHookError as e:
+            self.eval_hooks_manager.run_error(context, e)
         except Exception as e:
             logger.error(f"DevCycle: Error evaluating variable: {e}")
             return Variable.create_default_variable(
                 key=key, default_value=default_value
             )
+        finally:
+            self.eval_hooks_manager.run_finally(context, variable)
 
         variable.defaultValue = default_value
 
@@ -189,6 +221,12 @@ def close(self) -> None:
         # Cloud client doesn't need to release any resources
         logger.debug("DevCycle: Cloud client closed")
 
+    def add_hook(self, hook: EvalHook) -> None:
+        self.eval_hooks_manager.add_hook(hook)
+
+    def clear_hooks(self) -> None:
+        self.eval_hooks_manager.clear_hooks()
+
 
 def _validate_sdk_key(sdk_key: str) -> None:
     if sdk_key is None or len(sdk_key) == 0:

devcycle_python_sdk/local_client.py

@@ -8,8 +8,15 @@
 from devcycle_python_sdk.api.local_bucketing import LocalBucketing
 from devcycle_python_sdk.exceptions import VariableTypeMismatchError
 from devcycle_python_sdk.managers.config_manager import EnvironmentConfigManager
+from devcycle_python_sdk.managers.eval_hooks_manager import (
+    EvalHooksManager,
+    BeforeHookError,
+    AfterHookError,
+)
 from devcycle_python_sdk.managers.event_queue_manager import EventQueueManager
 from devcycle_python_sdk.models.bucketed_config import BucketedConfig
+from devcycle_python_sdk.models.eval_hook import EvalHook
+from devcycle_python_sdk.models.eval_hook_context import HookContext
 from devcycle_python_sdk.models.event import DevCycleEvent, EventType
 from devcycle_python_sdk.models.feature import Feature
 from devcycle_python_sdk.models.platform_data import default_platform_data
@@ -51,6 +58,7 @@ def __init__(self, sdk_key: str, options: DevCycleLocalOptions):
         )
 
         self._openfeature_provider: Optional[DevCycleProvider] = None
+        self.eval_hooks_manager = EvalHooksManager(self.options.eval_hooks)
 
     def get_sdk_platform(self) -> str:
         return "Local"
@@ -133,18 +141,44 @@ def variable(self, user: DevCycleUser, key: str, default_value: Any) -> Variable
                 )
             return Variable.create_default_variable(key, default_value)
 
+        context = HookContext(key, user, default_value)
+        variable = Variable.create_default_variable(
+            key=key, default_value=default_value
+        )
+
         try:
-            variable = self.local_bucketing.get_variable_for_user_protobuf(
+            before_hook_error = None
+            try:
+                changed_context = self.eval_hooks_manager.run_before(context)
+                if changed_context is not None:
+                    context = changed_context
+            except BeforeHookError as e:
+                before_hook_error = e
+            bucketed_variable = self.local_bucketing.get_variable_for_user_protobuf(
                 user, key, default_value
             )
-            if variable:
-                return variable
+            if bucketed_variable is not None:
+                variable = bucketed_variable
+
+            if before_hook_error is None:
+                self.eval_hooks_manager.run_after(context, variable)
+            else:
+                raise before_hook_error
         except VariableTypeMismatchError:
             logger.debug("DevCycle: Variable type mismatch, returning default value")
+            return variable
+        except BeforeHookError as e:
+            self.eval_hooks_manager.run_error(context, e)
+            return variable
+        except AfterHookError as e:
+            self.eval_hooks_manager.run_error(context, e)
+            return variable
         except Exception as e:
             logger.warning(f"DevCycle: Error retrieving variable for user: {e}")
-
-        return Variable.create_default_variable(key, default_value)
+            return variable
+        finally:
+            self.eval_hooks_manager.run_finally(context, variable)
+        return variable
 
     def _generate_bucketed_config(self, user: DevCycleUser) -> BucketedConfig:
         """
@@ -169,8 +203,6 @@ def all_variables(self, user: DevCycleUser) -> Dict[str, Variable]:
             )
             return {}
 
-        variable_map: Dict[str, Variable] = {}
-
         try:
             return self.local_bucketing.generate_bucketed_config(user).variables
         except Exception as e:
@@ -179,8 +211,6 @@ def all_variables(self, user: DevCycleUser) -> Dict[str, Variable]:
             )
             return {}
 
-        return variable_map
-
     def all_features(self, user: DevCycleUser) -> Dict[str, Feature]:
         """
         Returns all segmented and bucketed features for a user.  This method will return an empty map if the client has not been initialized or if the user is not bucketed into any features
@@ -234,6 +264,12 @@ def close(self) -> None:
         self.config_manager.close()
         self.event_queue_manager.close()
 
+    def add_hook(self, eval_hook: EvalHook) -> None:
+        self.eval_hooks_manager.add_hook(eval_hook)
+
+    def clear_hooks(self) -> None:
+        self.eval_hooks_manager.clear_hooks()
+
 
 def _validate_sdk_key(sdk_key: str) -> None:
     if sdk_key is None or len(sdk_key) == 0:

devcycle_python_sdk/managers/eval_hooks_manager.py

@@ -0,0 +1,73 @@
+from typing import List, Optional
+
+from devcycle_python_sdk.models.eval_hook import EvalHook
+from devcycle_python_sdk.models.eval_hook_context import HookContext
+from devcycle_python_sdk.models.variable import Variable
+from devcycle_python_sdk.options import logger
+
+
+class BeforeHookError(Exception):
+    """Exception raised when a before hook fails"""
+
+    def __init__(self, message: str, original_error: Exception):
+        self.message = message
+        self.original_error = original_error
+        super().__init__(self.message)
+
+
+class AfterHookError(Exception):
+    """Exception raised when an after hook fails"""
+
+    def __init__(self, message: str, original_error: Exception):
+        self.message = message
+        self.original_error = original_error
+        super().__init__(self.message)
+
+
+class EvalHooksManager:
+    def __init__(self, hooks: Optional[List[EvalHook]] = None):
+        self.hooks: List[EvalHook] = hooks if hooks is not None else []
+
+    def add_hook(self, hook: EvalHook) -> None:
+        """Add an evaluation hook to be executed"""
+        self.hooks.append(hook)
+
+    def clear_hooks(self) -> None:
+        """Clear all evaluation hooks"""
+        self.hooks = []
+
+    def run_before(self, context: HookContext) -> Optional[HookContext]:
+        """Run before hooks and return modified context if any"""
+        modified_context = context
+        for hook in self.hooks:
+            try:
+                result = hook.before(modified_context)
+                if result:
+                    modified_context = result
+            except Exception as e:
+                raise BeforeHookError(f"Before hook failed: {e}", e)
+        return modified_context
+
+    def run_after(self, context: HookContext, variable: Variable) -> None:
+        """Run after hooks with the evaluation result"""
+        for hook in self.hooks:
+            try:
+                hook.after(context, variable)
+            except Exception as e:
+                raise AfterHookError(f"After hook failed: {e}", e)
+
+    def run_finally(self, context: HookContext, variable: Optional[Variable]) -> None:
+        """Run finally hooks after evaluation completes"""
+        for hook in self.hooks:
+            try:
+                hook.on_finally(context, variable)
+            except Exception as e:
+                logger.error(f"Error running finally hook: {e}")
+
+    def run_error(self, context: HookContext, error: Exception) -> None:
+        """Run error hooks when an error occurs"""
+        for hook in self.hooks:
+            try:
+                hook.error(context, error)
+            except Exception as e:
+                logger.error(f"Error running error hook: {e}")

devcycle_python_sdk/models/bucketed_config.py

@@ -1,4 +1,3 @@
-# ruff: noqa: N815
 from dataclasses import dataclass
 from typing import Dict, List
 from typing import Optional

devcycle_python_sdk/models/eval_hook.py

@@ -0,0 +1,18 @@
+from typing import Callable, Optional
+
+from devcycle_python_sdk.models.eval_hook_context import HookContext
+from devcycle_python_sdk.models.variable import Variable
+
+
+class EvalHook:
+    def __init__(
+        self,
+        before: Callable[[HookContext], Optional[HookContext]],
+        after: Callable[[HookContext, Variable], None],
+        on_finally: Callable[[HookContext, Optional[Variable]], None],
+        error: Callable[[HookContext, Exception], None],
+    ):
+        self.before = before
+        self.after = after
+        self.on_finally = on_finally
+        self.error = error

devcycle_python_sdk/models/eval_hook_context.py

@@ -0,0 +1,10 @@
+from typing import Any
+
+from devcycle_python_sdk.models.user import DevCycleUser
+
+
+class HookContext:
+    def __init__(self, key: str, user: DevCycleUser, default_value: Any):
+        self.key = key
+        self.default_value = default_value
+        self.user = user

devcycle_python_sdk/options.py

@@ -1,5 +1,7 @@
 import logging
-from typing import Callable, Optional, Dict, Any
+from typing import Callable, Optional, Dict, Any, List
+
+from devcycle_python_sdk.models.eval_hook import EvalHook
 
 logger = logging.getLogger(__name__)
 
@@ -16,12 +18,14 @@ def __init__(
         request_timeout: int = 5,  # seconds
         request_retries: int = 5,
         retry_delay: int = 200,  # milliseconds
+        eval_hooks: Optional[List[EvalHook]] = None,
     ):
         self.enable_edge_db = enable_edge_db
         self.bucketing_api_uri = bucketing_api_uri
         self.request_timeout = request_timeout
         self.request_retries = request_retries
         self.retry_delay = retry_delay
+        self.eval_hooks = eval_hooks if eval_hooks is not None else []
 
 
 class DevCycleLocalOptions:
@@ -47,6 +51,7 @@ def __init__(
         disable_custom_event_logging: bool = False,
         enable_beta_realtime_updates: bool = False,
         disable_realtime_updates: bool = False,
+        eval_hooks: Optional[List[EvalHook]] = None,
     ):
         self.events_api_uri = events_api_uri
         self.config_cdn_uri = config_cdn_uri
@@ -69,6 +74,8 @@ def __init__(
                 "DevCycle: `enable_beta_realtime_updates` is deprecated and will be removed in a future release.",
             )
 
+        self.eval_hooks = eval_hooks if eval_hooks is not None else []
+
         if self.flush_event_queue_size >= self.max_event_queue_size:
             logger.warning(
                 f"DevCycle: flush_event_queue_size: {self.flush_event_queue_size} must be smaller than max_event_queue_size: {self.max_event_queue_size}"