def depth_tooltip(cls, depth: Optional[int]) -> str:
        """Returns text tooltip for given mempool depth (in vbytes)."""
        if depth is None:
            return "unknown from tip"
        depth_mb = cls.get_depth_mb_str(depth)
        return _("{} from tip").format(depth_mb)
Returns text tooltip for given mempool depth (in vbytes).
electrum/fee_policy.py