code: def is_shard(self, dim: Optional[int] = None) -> bool:
      is_shard_instance = isinstance(self, Shard)
      if dim is not None and is_shard_instance:
          return cast(Shard, self).dim == dim
      else:
          return is_shard_instance
  
imports: from dataclasses import dataclass
  from typing import Any, cast, List, NamedTuple, Optional, Tuple
  import torch
  import torch.distributed._functional_collectives
  import torch.distributed.distributed_c10d
  from torch.distributed._tensor._collective_utils import mesh_broadcast, mesh_scatter
  from torch.distributed.device_mesh import DeviceMesh
label_desc: Use image node_id 1 for calling the Placement obj's underlying member method code with example usage: obj.is_shard(dim) and returns: unknown, is_shard_instance