class_docstr: A container to hold all callbacks, and trigger them iteratively.
  
  This is only used by the base trainer to run all the callbacks.
  Users do not need to use this class.
code: def _setup_graph(self):
      with tf.name_scope(None):  # clear the name scope
          for cb in self.cbs:
              cb.setup_graph(self.trainer)
  
imports: import traceback
  from contextlib import contextmanager
  from time import perf_counter
  from ..compat import tfv1
  from ..utils import logger
  from ..utils.utils import humanize_time_delta
  from .base import Callback
  from .hooks import CallbackToHook
label_desc: Use image node_id 2 for calling the Callbacks obj's underlying member method code with example usage: obj._setup_graph() without return types