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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def crop(self, box):
 """ Cropss a rectangular region from this bounding box. The box is a 4-tuple defining the left, upper, right, and lower pixel coordinate. """

        xmin, ymin, xmax, ymax = self._split_into_xyxy()
        w, h = box[2] - box[0], box[3] - box[1]
        cropped_xmin = (xmin - box[0]).clamp(min=0, max=w)
        cropped_ymin = (ymin - box[1]).clamp(min=0, max=h)
        cropped_xmax = (xmax - box[0]).clamp(min=0, max=w)
        cropped_ymax = (ymax - box[1]).clamp(min=0, max=h)

        # TODO should I filter empty boxes here?
        if False:
            is_empty = (cropped_xmin == cropped_xmax) | (cropped_ymin == cropped_ymax)

        cropped_box = torch.cat(
            (cropped_xmin, cropped_ymin, cropped_xmax, cropped_ymax), dim=-1
        )
        bbox = BoxList(cropped_box, (w, h), mode="xyxy")
        # bbox._copy_extra_fields(self)
        for k, v in self.extra_fields.items():
            if not isinstance(v, torch.Tensor):
                v = v.crop(box)
            bbox.add_field(k, v)
        return bbox.convert(self.mode)