code: def __len__(self) -> int:
      return len(self.transitions)
  
imports: from abc import ABC, abstractmethod
  from dataclasses import asdict, dataclass, field, fields
  from typing import Any, Callable, Dict, List, Optional, Union
  import numpy
  import reagent.core.types
  import torch
  import torch.nn.functional
label_desc: Use image node_id 2 for calling the Trajectory obj's underlying member method code with example usage: obj.__len__() and returns: len