pipelines.py 文件源码

def _best_transform_from(self, source_type: Type[S], target_types: Iterable[Type]) -> Tuple[Callable[[S], Any], Type, int]:
        best = None
        best_cost = _MAX_TRANSFORM_COST
        to_type = None
        for target_type in target_types:
            try:
                transform, cost = self._transform(source_type, target_type)
                if cost < best_cost:
                    best = transform
                    best_cost = cost
                    to_type = target_type
            except NoConversionError:
                pass
        if best is None:
            raise NoConversionError("Pipeline can't convert \"{source_type}\" to any of \"{target_types}\"".format(source_type=source_type, target_types=target_types))
        return best, to_type, best_cost