iterative tool handler process

src/strands/agent/agent.py

@@ -128,7 +128,7 @@ def caller(
                 }
 
                 # Execute the tool
-                tool_result = self._agent.tool_handler.process(
+                events = self._agent.tool_handler.process(
                     tool=tool_use,
                     model=self._agent.model,
                     system_prompt=self._agent.system_prompt,
@@ -137,6 +137,12 @@ def caller(
                     kwargs=kwargs,
                 )
 
+                try:
+                    while True:
+                        next(events)
+                except StopIteration as stop:
+                    tool_result = cast(ToolResult, stop.value)
+
                 if record_direct_tool_call is not None:
                     should_record_direct_tool_call = record_direct_tool_call
                 else:

src/strands/handlers/tool_handler.py

@@ -6,7 +6,7 @@
 from ..tools.registry import ToolRegistry
 from ..types.content import Messages
 from ..types.models import Model
-from ..types.tools import ToolConfig, ToolHandler, ToolUse
+from ..types.tools import ToolConfig, ToolGenerator, ToolHandler, ToolUse
 
 logger = logging.getLogger(__name__)
 
@@ -35,7 +35,7 @@ def process(
         messages: Messages,
         tool_config: ToolConfig,
         kwargs: dict[str, Any],
-    ) -> Any:
+    ) -> ToolGenerator:
         """Process a tool invocation.
 
         Looks up the tool in the registry and invokes it with the provided parameters.
@@ -48,8 +48,11 @@ def process(
             tool_config: Configuration for the tool.
             kwargs: Additional keyword arguments passed to the tool.
 
+        Yields:
+            Events of the tool invocation.
+
         Returns:
-            The result of the tool invocation, or an error response if the tool fails or is not found.
+            The final tool result or an error response if the tool fails or is not found.
         """
         logger.debug("tool=<%s> | invoking", tool)
         tool_use_id = tool["toolUseId"]
@@ -82,7 +85,9 @@ def process(
                 }
             )
 
-            return tool_func.invoke(tool, **kwargs)
+            result = tool_func.invoke(tool, **kwargs)
+            yield {"result": result}  # Placeholder until tool_func becomes a generator from which we can yield from
+            return result
 
         except Exception as e:
             logger.exception("tool_name=<%s> | failed to process tool", tool_name)

src/strands/tools/executor.py

@@ -13,13 +13,13 @@
 from ..tools.tools import InvalidToolUseNameException, validate_tool_use
 from ..types.content import Message
 from ..types.event_loop import ParallelToolExecutorInterface
-from ..types.tools import ToolResult, ToolUse
+from ..types.tools import ToolGenerator, ToolResult, ToolUse
 
 logger = logging.getLogger(__name__)
 
 
 def run_tools(
-    handler: Callable[[ToolUse], ToolResult],
+    handler: Callable[[ToolUse], Generator[dict[str, Any], None, ToolResult]],
     tool_uses: list[ToolUse],
     event_loop_metrics: EventLoopMetrics,
     invalid_tool_use_ids: list[str],
@@ -44,16 +44,15 @@ def run_tools(
         Events of the tool invocations. Tool results are appended to `tool_results`.
     """
 
-    def handle(tool: ToolUse) -> Generator[dict[str, Any], None, ToolResult]:
+    def handle(tool: ToolUse) -> ToolGenerator:
         tracer = get_tracer()
         tool_call_span = tracer.start_tool_call_span(tool, parent_span)
 
         tool_name = tool["name"]
         tool_trace = Trace(f"Tool: {tool_name}", parent_id=cycle_trace.id, raw_name=tool_name)
         tool_start_time = time.time()
 
-        result = handler(tool)
-        yield {"result": result}  # Placeholder until handler becomes a generator from which we can yield from
+        result = yield from handler(tool)
 
         tool_success = result.get("status") == "success"
         tool_duration = time.time() - tool_start_time
@@ -74,14 +73,14 @@ def work(
     ) -> ToolResult:
         events = handle(tool)
 
-        while True:
-            try:
+        try:
+            while True:
                 event = next(events)
                 worker_queue.put((worker_id, event))
                 worker_event.wait()
 
-            except StopIteration as stop:
-                return cast(ToolResult, stop.value)
+        except StopIteration as stop:
+            return cast(ToolResult, stop.value)
 
     tool_uses = [tool_use for tool_use in tool_uses if tool_use.get("toolUseId") not in invalid_tool_use_ids]
 

src/strands/types/tools.py

@@ -6,7 +6,7 @@
 """
 
 from abc import ABC, abstractmethod
-from typing import TYPE_CHECKING, Any, Dict, List, Literal, Optional, Union
+from typing import TYPE_CHECKING, Any, Generator, Literal, Optional, Union
 
 from typing_extensions import TypedDict
 
@@ -90,7 +90,7 @@ class ToolResult(TypedDict):
         toolUseId: The unique identifier of the tool use request that produced this result.
     """
 
-    content: List[ToolResultContent]
+    content: list[ToolResultContent]
     status: ToolResultStatus
     toolUseId: str
 
@@ -122,9 +122,9 @@ class ToolChoiceTool(TypedDict):
 
 
 ToolChoice = Union[
-    Dict[Literal["auto"], ToolChoiceAuto],
-    Dict[Literal["any"], ToolChoiceAny],
-    Dict[Literal["tool"], ToolChoiceTool],
+    dict[Literal["auto"], ToolChoiceAuto],
+    dict[Literal["any"], ToolChoiceAny],
+    dict[Literal["tool"], ToolChoiceTool],
 ]
 """
 Configuration for how the model should choose tools.
@@ -135,6 +135,10 @@ class ToolChoiceTool(TypedDict):
 """
 
 
+ToolGenerator = Generator[dict[str, Any], None, ToolResult]
+"""Generator of tool events and a returned tool result."""
+
+
 class ToolConfig(TypedDict):
     """Configuration for tools in a model request.
 
@@ -143,7 +147,7 @@ class ToolConfig(TypedDict):
         toolChoice: Configuration for how the model should choose tools.
     """
 
-    tools: List[Tool]
+    tools: list[Tool]
     toolChoice: ToolChoice
 
 
@@ -250,7 +254,7 @@ def process(
         messages: "Messages",
         tool_config: ToolConfig,
         kwargs: dict[str, Any],
-    ) -> ToolResult:
+    ) -> ToolGenerator:
         """Process a tool use request and execute the tool.
 
         Args:
@@ -261,7 +265,10 @@ def process(
             tool_config: The tool configuration for the current session.
             kwargs: Additional context-specific arguments.
 
+        Yields:
+            Events of the tool invocation.
+
         Returns:
-            The result of the tool execution.
+            The final tool result.
         """
         ...

tests/conftest.py

@@ -68,3 +68,22 @@ def boto3_profile_path(boto3_profile, tmp_path, monkeypatch):
     monkeypatch.setenv("AWS_SHARED_CREDENTIALS_FILE", str(path))
 
     return path
+
+
+## Itertools
+
+
+@pytest.fixture(scope="session")
+def generate():
+    def generate(generator):
+        events = []
+
+        try:
+            while True:
+                event = next(generator)
+                events.append(event)
+
+        except StopIteration as stop:
+            return events, stop.value
+
+    return generate

tests/strands/agent/test_agent.py

@@ -771,7 +771,7 @@ def test_agent_init_with_no_model_or_model_id():
 
 
 def test_agent_tool_no_parameter_conflict(agent, tool_registry, mock_randint):
-    agent.tool_handler = unittest.mock.Mock()
+    agent.tool_handler = unittest.mock.Mock(process=unittest.mock.Mock(return_value=iter([])))
 
     @strands.tools.tool(name="system_prompter")
     def function(system_prompt: str) -> str:
@@ -798,7 +798,7 @@ def function(system_prompt: str) -> str:
 
 
 def test_agent_tool_with_name_normalization(agent, tool_registry, mock_randint):
-    agent.tool_handler = unittest.mock.Mock()
+    agent.tool_handler = unittest.mock.Mock(process=unittest.mock.Mock(return_value=iter([])))
 
     tool_name = "system-prompter"
 
@@ -826,8 +826,6 @@ def function(system_prompt: str) -> str:
 
 
 def test_agent_tool_with_no_normalized_match(agent, tool_registry, mock_randint):
-    agent.tool_handler = unittest.mock.Mock()
-
     mock_randint.return_value = 1
 
     with pytest.raises(AttributeError) as err:

tests/strands/handlers/test_tool_handler.py

@@ -26,29 +26,33 @@ def identity(a: int) -> int:
     return {"toolUseId": "identity", "name": "identity", "input": {"a": 1}}
 
 
-def test_process(tool_handler, tool_use_identity):
-    tru_result = tool_handler.process(
+def test_process(tool_handler, tool_use_identity, generate):
+    process = tool_handler.process(
         tool_use_identity,
         model=unittest.mock.Mock(),
         system_prompt="p1",
         messages=[],
         tool_config={},
         kwargs={},
     )
+
+    _, tru_result = generate(process)
     exp_result = {"toolUseId": "identity", "status": "success", "content": [{"text": "1"}]}
 
     assert tru_result == exp_result
 
 
-def test_process_missing_tool(tool_handler):
-    tru_result = tool_handler.process(
+def test_process_missing_tool(tool_handler, generate):
+    process = tool_handler.process(
         tool={"toolUseId": "missing", "name": "missing", "input": {}},
         model=unittest.mock.Mock(),
         system_prompt="p1",
         messages=[],
         tool_config={},
         kwargs={},
     )
+
+    _, tru_result = generate(process)
     exp_result = {
         "toolUseId": "missing",
         "status": "error",

tests/strands/tools/test_executor.py

@@ -18,6 +18,7 @@ def moto_autouse(moto_env):
 @pytest.fixture
 def tool_handler(request):
     def handler(tool_use):
+        yield {"event": "abc"}
         return {
             **params,
             "toolUseId": tool_use["toolUseId"],
@@ -102,7 +103,9 @@ def test_run_tools(
         cycle_trace,
         parallel_tool_executor,
     )
-    list(stream)
+
+    tru_events = list(stream)
+    exp_events = [{"event": "abc"}]
 
     tru_results = tool_results
     exp_results = [
@@ -117,7 +120,7 @@ def test_run_tools(
         },
     ]
 
-    assert tru_results == exp_results
+    assert tru_events == exp_events and tru_results == exp_results
 
 
 @pytest.mark.parametrize("invalid_tool_use_ids", [["t1"]], indirect=True)