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]
  
imports: import uuid
  import sys
  from ...envs.utils import _module_available, _compare_version, _get_version
  from ...envs import get_global_rank
  from .utils import is_notebook
  from ..log import logger
  import operator
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