langchain/chains/sequential.py/SimpleSequentialChain/_acall
class SimpleSequentialChain:    async def _acall(
        self,
        inputs: Dict[str, Any],
        run_manager: Optional[AsyncCallbackManagerForChainRun] = None,
    ) -> Dict[str, Any]:
        _run_manager = run_manager or AsyncCallbackManagerForChainRun.get_noop_manager()
        callbacks = _run_manager.get_child()
        _input = inputs[self.input_key]
        color_mapping = get_color_mapping([str(i) for i in range(len(self.chains))])
        for i, chain in enumerate(self.chains):
            _input = await chain.arun(_input, callbacks=callbacks)
            if self.strip_outputs:
                _input = _input.strip()
            await _run_manager.on_text(
                _input, color=color_mapping[str(i)], end="\n", verbose=self.verbose
            )
        return {self.output_key: _input}