bedrock: allow empty system prompt (#1405)

Author: Kludex

pydantic_ai_slim/pydantic_ai/models/bedrock.py

@@ -10,6 +10,7 @@
 
 import anyio
 import anyio.to_thread
+from mypy_boto3_bedrock_runtime.type_defs import ConverseRequestTypeDef, SystemContentBlockTypeDef
 from typing_extensions import ParamSpec, assert_never
 
 from pydantic_ai import _utils, result
@@ -258,20 +259,19 @@ async def _messages_create(
         else:
             tool_choice = {'auto': {}}
 
-        system_prompt, bedrock_messages = await self._map_message(messages)
+        system_prompt, bedrock_messages = await self._map_messages(messages)
         inference_config = self._map_inference_config(model_settings)
 
-        params = {
+        params: ConverseRequestTypeDef = {
             'modelId': self.model_name,
             'messages': bedrock_messages,
-            'system': [{'text': system_prompt}],
+            'system': system_prompt,
             'inferenceConfig': inference_config,
-            **(
-                {'toolConfig': {'tools': tools, **({'toolChoice': tool_choice} if tool_choice else {})}}
-                if tools
-                else {}
-            ),
         }
+        if tools:
+            params['toolConfig'] = {'tools': tools}
+            if tool_choice:
+                params['toolConfig']['toolChoice'] = tool_choice
 
         if stream:
             model_response = await anyio.to_thread.run_sync(functools.partial(self.client.converse_stream, **params))
@@ -299,15 +299,17 @@ def _map_inference_config(
 
         return inference_config
 
-    async def _map_message(self, messages: list[ModelMessage]) -> tuple[str, list[MessageUnionTypeDef]]:
+    async def _map_messages(
+        self, messages: list[ModelMessage]
+    ) -> tuple[list[SystemContentBlockTypeDef], list[MessageUnionTypeDef]]:
         """Just maps a `pydantic_ai.Message` to the Bedrock `MessageUnionTypeDef`."""
-        system_prompt: str = ''
+        system_prompt: list[SystemContentBlockTypeDef] = []
         bedrock_messages: list[MessageUnionTypeDef] = []
         for m in messages:
             if isinstance(m, ModelRequest):
                 for part in m.parts:
                     if isinstance(part, SystemPromptPart):
-                        system_prompt += part.content
+                        system_prompt.append({'text': part.content})
                     elif isinstance(part, UserPromptPart):
                         bedrock_messages.extend(await self._map_user_prompt(part))
                     elif isinstance(part, ToolReturnPart):

tests/models/cassettes/test_bedrock/test_bedrock_empty_system_prompt.yaml

@@ -0,0 +1,48 @@
+interactions:
+- request:
+    body: '{"messages": [{"role": "user", "content": [{"text": "What is the capital of France?"}]}], "system": [], "inferenceConfig":
+      {}}'
+    headers:
+      amz-sdk-invocation-id:
+      - !!binary |
+        ZjdiY2FlMDgtYzQxMi00OTgxLWJiOGUtNzZiN2QzNGRmMDM2
+      amz-sdk-request:
+      - !!binary |
+        YXR0ZW1wdD0x
+      content-length:
+      - '126'
+      content-type:
+      - !!binary |
+        YXBwbGljYXRpb24vanNvbg==
+    method: POST
+    uri: https://bedrock-runtime.us-east-1.amazonaws.com/model/us.amazon.nova-micro-v1%3A0/converse
+  response:
+    headers:
+      connection:
+      - keep-alive
+      content-length:
+      - '784'
+      content-type:
+      - application/json
+    parsed_body:
+      metrics:
+        latencyMs: 1406
+      output:
+        message:
+          content:
+          - text: The capital of France is Paris. Paris, officially known as "Ville de Paris," is not only the capital city
+              but also the most populous city in France. It is located in the northern central part of the country along the
+              Seine River. Paris is a major global city, renowned for its cultural, political, economic, and social influence.
+              It is famous for its landmarks such as the Eiffel Tower, the Louvre Museum, Notre-Dame Cathedral, and the Champs-Élysées,
+              among many other historic and modern attractions. The city has played a significant role in the history of art,
+              fashion, gastronomy, and science.
+          role: assistant
+      stopReason: end_turn
+      usage:
+        inputTokens: 7
+        outputTokens: 126
+        totalTokens: 133
+    status:
+      code: 200
+      message: OK
+version: 1

tests/models/test_bedrock.py

@@ -468,3 +468,13 @@ async def test_text_as_binary_content_input(allow_model_requests: None, bedrock_
 
 Since this is a test document, it probably doesn't contain any meaningful or specific information beyond what is necessary to serve its testing purpose. If you have specific questions about the format, structure, or any particular element within the document, feel free to ask!\
 """)
+
+
+@pytest.mark.vcr()
+async def test_bedrock_empty_system_prompt(allow_model_requests: None, bedrock_provider: BedrockProvider):
+    m = BedrockConverseModel('us.amazon.nova-micro-v1:0', provider=bedrock_provider)
+    agent = Agent(m)
+    result = await agent.run('What is the capital of France?')
+    assert result.data == snapshot(
+        'The capital of France is Paris. Paris, officially known as "Ville de Paris," is not only the capital city but also the most populous city in France. It is located in the northern central part of the country along the Seine River. Paris is a major global city, renowned for its cultural, political, economic, and social influence. It is famous for its landmarks such as the Eiffel Tower, the Louvre Museum, Notre-Dame Cathedral, and the Champs-Élysées, among many other historic and modern attractions. The city has played a significant role in the history of art, fashion, gastronomy, and science.'
+    )