Add {SamplingMessage,CreateMessageResult}.content_as_list + update usages

Author: ochafik

README.md

@@ -886,10 +886,9 @@ async def generate_poem(topic: str, ctx: Context[ServerSession, None]) -> str:
         max_tokens=100,
     )
 
-    content = result.content[0] if isinstance(result.content, list) else result.content
-    if content.type == "text":
-        return content.text
-    return str(content)
+    if all(c.type == "text" for c in result.content_as_list):
+        return '\n'.join(c.text for c in result.content_as_list if c.type == "text")
+    return str(result.content)
 ```
 
 _Full example: [examples/snippets/servers/sampling.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/servers/sampling.py)_

src/mcp/types.py

@@ -864,6 +864,12 @@ class SamplingMessage(BaseModel):
     """
     model_config = ConfigDict(extra="allow")
 
+    @property
+    def content_as_list(self) -> list[SamplingMessageContentBlock]:
+        """Returns the content as a list of content blocks, regardless of whether
+        it was originally a single block or a list."""
+        return self.content if isinstance(self.content, list) else [self.content]
+
 
 class EmbeddedResource(BaseModel):
     """
@@ -1232,6 +1238,12 @@ class CreateMessageResult(Result):
     'toolUse' indicates the model wants to use a tool.
     """
 
+    @property
+    def content_as_list(self) -> list[SamplingMessageContentBlock]:
+        """Returns the content as a list of content blocks, regardless of whether
+        it was originally a single block or a list."""
+        return self.content if isinstance(self.content, list) else [self.content]
+
 
 class ResourceTemplateReference(BaseModel):
     """A reference to a resource or resource template definition."""

tests/shared/test_streamable_http.py

@@ -210,10 +210,16 @@ async def handle_call_tool(name: str, args: dict[str, Any]) -> list[TextContent]
                 )
 
                 # Return the sampling result in the tool response
-                content = (
-                    sampling_result.content[0] if isinstance(sampling_result.content, list) else sampling_result.content
-                )
-                response = content.text if content.type == "text" else None
+                if isinstance(sampling_result.content, list):
+                    response = (
+                        sampling_result.content[0].text
+                        if sampling_result.content and sampling_result.content[0].type == "text"
+                        else None
+                    )
+                elif sampling_result.content.type == "text":
+                    response = sampling_result.content.text
+                else:
+                    response = None
                 return [
                     TextContent(
                         type="text",
@@ -1242,12 +1248,13 @@ async def sampling_callback(
         nonlocal sampling_callback_invoked, captured_message_params
         sampling_callback_invoked = True
         captured_message_params = params
-        msg_content = (
-            params.messages[0].content[0]
-            if isinstance(params.messages[0].content, list)
-            else params.messages[0].content
-        )
-        message_received = msg_content.text if msg_content.type == "text" else None
+        msg_content = params.messages[0].content
+        if isinstance(msg_content, list):
+            message_received = msg_content[0].text if msg_content and msg_content[0].type == "text" else None
+        elif msg_content.type == "text":
+            message_received = msg_content.text
+        else:
+            message_received = None
 
         return types.CreateMessageResult(
             role="assistant",