fix: Migrate Mistral structured_output to an iterator (strands-agents#305)

Mistral was merged after the latest iterator changes (strands-agents#291) so it didn't have the latest and greatest

---------

Co-authored-by: Mackenzie Zastrow <zastrowm@users.noreply.github.com>

Author: zastrowm

src/strands/models/mistral.py

@@ -6,7 +6,7 @@
 import base64
 import json
 import logging
-from typing import Any, Callable, Dict, Iterable, List, Optional, Type, TypeVar, Union
+from typing import Any, Callable, Dict, Generator, Iterable, List, Optional, Type, TypeVar, Union
 
 from mistralai import Mistral
 from pydantic import BaseModel
@@ -472,7 +472,7 @@ def stream(self, request: dict[str, Any]) -> Iterable[dict[str, Any]]:
     @override
     def structured_output(
         self, output_model: Type[T], prompt: Messages, callback_handler: Optional[Callable] = None
-    ) -> T:
+    ) -> Generator[dict[str, Union[T, Any]], None, None]:
         """Get structured output from the model.
 
         Args:
@@ -507,7 +507,8 @@ def structured_output(
                     arguments = json.loads(tool_call.function.arguments)
                 else:
                     arguments = tool_call.function.arguments
-                return output_model(**arguments)
+                yield {"output": output_model(**arguments)}
+                return
             except (json.JSONDecodeError, TypeError, ValueError) as e:
                 raise ValueError(f"Failed to parse tool call arguments into model: {e}") from e
 

tests/strands/models/test_mistral.py

@@ -1,5 +1,6 @@
 import unittest.mock
 
+import pydantic
 import pytest
 
 import strands
@@ -58,6 +59,15 @@ def system_prompt():
     return "You are a helpful assistant"
 
 
+@pytest.fixture
+def test_output_model_cls():
+    class TestOutputModel(pydantic.BaseModel):
+        name: str
+        age: int
+
+    return TestOutputModel
+
+
 def test__init__model_configs(mistral_client, model_id, max_tokens):
     _ = mistral_client
 
@@ -440,35 +450,24 @@ def test_stream_other_error(mistral_client, model):
         list(model.stream({}))
 
 
-def test_structured_output_success(mistral_client, model):
-    from pydantic import BaseModel
-
-    class TestModel(BaseModel):
-        name: str
-        age: int
+def test_structured_output_success(mistral_client, model, test_output_model_cls):
+    messages = [{"role": "user", "content": [{"text": "Extract data"}]}]
 
-    # Mock successful response
     mock_response = unittest.mock.Mock()
     mock_response.choices = [unittest.mock.Mock()]
     mock_response.choices[0].message.tool_calls = [unittest.mock.Mock()]
     mock_response.choices[0].message.tool_calls[0].function.arguments = '{"name": "John", "age": 30}'
 
     mistral_client.chat.complete.return_value = mock_response
 
-    prompt = [{"role": "user", "content": [{"text": "Extract data"}]}]
-    result = model.structured_output(TestModel, prompt)
-
-    assert isinstance(result, TestModel)
-    assert result.name == "John"
-    assert result.age == 30
-
+    stream = model.structured_output(test_output_model_cls, messages)
 
-def test_structured_output_no_tool_calls(mistral_client, model):
-    from pydantic import BaseModel
+    tru_result = list(stream)[-1]
+    exp_result = {"output": test_output_model_cls(name="John", age=30)}
+    assert tru_result == exp_result
 
-    class TestModel(BaseModel):
-        name: str
 
+def test_structured_output_no_tool_calls(mistral_client, model, test_output_model_cls):
     mock_response = unittest.mock.Mock()
     mock_response.choices = [unittest.mock.Mock()]
     mock_response.choices[0].message.tool_calls = None
@@ -478,15 +477,11 @@ class TestModel(BaseModel):
     prompt = [{"role": "user", "content": [{"text": "Extract data"}]}]
 
     with pytest.raises(ValueError, match="No tool calls found in response"):
-        model.structured_output(TestModel, prompt)
-
+        stream = model.structured_output(test_output_model_cls, prompt)
+        next(stream)
 
-def test_structured_output_invalid_json(mistral_client, model):
-    from pydantic import BaseModel
-
-    class TestModel(BaseModel):
-        name: str
 
+def test_structured_output_invalid_json(mistral_client, model, test_output_model_cls):
     mock_response = unittest.mock.Mock()
     mock_response.choices = [unittest.mock.Mock()]
     mock_response.choices[0].message.tool_calls = [unittest.mock.Mock()]
@@ -497,4 +492,5 @@ class TestModel(BaseModel):
     prompt = [{"role": "user", "content": [{"text": "Extract data"}]}]
 
     with pytest.raises(ValueError, match="Failed to parse tool call arguments into model"):
-        model.structured_output(TestModel, prompt)
+        stream = model.structured_output(test_output_model_cls, prompt)
+        next(stream)