code: def __call__(cls, *args, **kwargs):
      if cls not in cls._instances:
          cls._instances[cls] = super(_Singleton, cls).__call__(
              *args, **kwargs
          )
      return cls._instances[cls]
  
file_path: avalanche/avalanche/training/determinism/rng_manager.py
imports: import random
  from collections import OrderedDict
  from typing import Any, Dict, Type
  import numpy
  import torch
  from avalanche.training.determinism.cuda_rng import cuda_rng_seed, cuda_rng_save_state, cuda_rng_load_state, cuda_rng_step, cpu_rng_seed
label_desc: Use image node_id 1 for calling the _Singleton obj's underlying member method code with example usage: obj.__call__(cls) and returns: cls