def __getitem__(self, item: Union[int, slice, torch.BoolTensor]) -> "Instances":
        """
        Args:
            item: an index-like object and will be used to index all the fields.

        Returns:
            If `item` is a string, return the data in the corresponding field.
            Otherwise, returns an `Instances` where all fields are indexed by `item`.
        """
        if type(item) == int:
            if item >= len(self) or item < -len(self):
                raise IndexError("Instances index out of range!")
            else:
                item = slice(item, None, len(self))

        ret = Instances(self._image_size)
        for k, v in self._fields.items():
            ret.set(k, v[item])
        return ret

        Args:
            item: an index-like object and will be used to index all the fields.

        Returns:
            If `item` is a string, return the data in the corresponding field.
            Otherwise, returns an `Instances` where all fields are indexed by `item`.
        
video_chat_with_StableLM/models/grit_src/third_party/CenterNet2/detectron2/structures/instances.py