Subclassing BaseTool: args_schema always None

[danielchalef]

Following the example here, when subclassing BaseTool, args_schema is always None.

langchain 0.0.145

class SendMessageInput(BaseModel):
    email: str = Field(description="email")
    message: str = Field(description="the message to send")


class SendMessageTool(BaseTool):
    name = "send_message_tool"
    description = "useful for when you need to send a message to a human"
    args_schema = SendMessageInput

    def _run(self, query: str) -> str:
        """Use the tool."""
        return f"Sent {query}"

    async def _arun(self, query: str) -> str:
        """Use the tool asynchronously."""
        return f"Sent {query}"

In [4]: smt = SendMessageTool()
In [5]: smt.args_schema == None
Out[5]: True

[vowelparrot]

The immediate fix is that it works if you add the type hint in the subclass.

class SendMessageTool(BaseTool):
    name = "send_message_tool"
    description = "useful for when you need to send a message to a human"
    args_schema: Type[BaseModel] = SendMessageInput # NOTE THE ": Type[BaseModel]"

    def _run(self, query: str) -> str:
        """Use the tool."""
        return f"Sent {query}"

    async def _arun(self, query: str) -> str:
        """Use the tool asynchronously."""
        return f"Sent {query}"

We will work to fix this behavior. It's 'by design' in pydantic and dataclasses but I even if we improve the docs here, it'll be a frequent "gotcha" if it isn't fixed.

Thank you for contributing to the project!

[danielchalef]

Thanks. That's a nasty gotcha. Just cut a pr to update the notebook with a type hint: #3323