rohitg00/ai-engineering-from-scratch · error · ToolLoopError

response content must be a list

Error message

response content must be a list

What it means

Error "response content must be a list" thrown in rohitg00/ai-engineering-from-scratch.

Source

Thrown at certifications/claude/lessons/10-tool-use-and-agentic-loops/code/main.py:252

    def __init__(
        self,
        model: ScriptedModel,
        registry: ToolRegistry,
        approve: Callable[[Tool, dict[str, Any]], bool] = lambda _tool, _args: False,
        max_turns: int = 8,
    ) -> None:
        self.model = model
        self.registry = registry
        self.approve = approve
        self.max_turns = max_turns

    def run(self, request: str) -> tuple[str, list[dict[str, Any]]]:
        messages: list[dict[str, Any]] = [{"role": "user", "content": request}]
        for _ in range(self.max_turns):
            response = self.model.create(messages)
            blocks = response.get("content")
            if not isinstance(blocks, list):
                raise ToolLoopError("response content must be a list")
            messages.append({"role": "assistant", "content": copy.deepcopy(blocks)})
            reason = response.get("stop_reason")
            if reason == "end_turn":
                text = "".join(block.get("text", "") for block in blocks if block.get("type") == "text")
                return text, messages
            if reason != "tool_use":
                raise ToolLoopError(f"unsupported stop reason: {reason}")
            calls = [block for block in blocks if block.get("type") == "tool_use"]
            if not calls:
                raise ToolLoopError("tool_use stop without calls")
            results = [self.registry.execute(block, self.approve) for block in calls]
            messages.append({"role": "user", "content": results})
        raise ToolLoopError("maximum turns exceeded")


def demo() -> tuple[str, list[dict[str, Any]]]:
    add = Tool(
        "add",

View on GitHub (pinned to 39ea8a1c6d)

When it happens

Trigger: Thrown at certifications/claude/lessons/10-tool-use-and-agentic-loops/code/main.py:252 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of rohitg00/ai-engineering-from-scratch@39ea8a1c6d (2026-08-26). Data as JSON: /api/errors/4fe0688e00cc600f. Report an issue: GitHub.