code: def num_cached_keys(self) -> int:
      return len(self.cached_keys())
  
imports: import warnings
  from typing import List, Optional, Tuple
  import torch
  from torch_scatter import scatter_add, segment_csr
  from torch_sparse.utils import Final, index_sort
label_desc: Use image node_id 31 for calling the SparseStorage obj's underlying member method code with example usage: obj.num_cached_keys() and returns: len