code: def __len__(self) -> int:
      return len(self.data)
  
imports: import collections
  from typing import Any, Callable, Deque, Generic, List, Optional, Sequence, Tuple, TypeVar
  import numpy
  from pfrl.utils.random import sample_n_k
label_desc: Use image node_id 2 for calling the PrioritizedBuffer obj's underlying member method code with example usage: obj.__len__() and returns: len