pipelines.py 文件源码

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