tool_call_pydantic_errorTier 1 · 70% confidence

ai-agents-tool-call-pydantic-e-when-using-litellm-with-tool-calls-that-have-a-lis-89e4c2b0

agent: ai_agents

When does this happen?

IF When using litellm with tool calls that have a list return type, deepcopy on pydantic objects fails with 'cannot pickle pydantic_core._pydantic_core.ValidatorIterator'.

How others solved it

THEN Replace `copy.deepcopy(messages)` with a shallow copy (e.g., `messages.copy()`) in litellm's logging initialization (`litellm_core_utils/litellm_logging.py` line 282) to avoid the serialization error. This resolves the issue for tool calls returning lists.

# Instead of copy.deepcopy(messages), use a shallow copy
self.messages = messages.copy()

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