class_docstr: A regular replay buffer which stores transition without any additional structure
docstr: Get the number of transitions in the ER
docstr_tok: ["Get","the","number","of","transitions","in","the","ER"]
code: def num_transitions(self) -> int:
      """
      Get the number of transitions in the ER
      """
      return len(self.transitions)
  
imports: from typing import List, Tuple, Union
  import pickle
  import random
  import math
  import numpy
  from rl_coach.core_types import Transition
  from rl_coach.logger import screen
  from rl_coach.memories.memory import Memory, MemoryGranularity, MemoryParameters
  from rl_coach.utils import ReaderWriterLock, ProgressBar
label_desc: Use image node_id 3 for calling the ExperienceReplay obj's underlying member method code with example usage: obj.num_transitions() and returns: len