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.
docstr: Args:
      cbs(list): a list of :class:`Callback` instances.
docstr_tok: ["Args",":","cbs","(","list",")",":","a","list","of",":","class",":","`","Callback","`","instances","."]
code: def __init__(self, cbs):
      """
      Args:
          cbs(list): a list of :class:`Callback` instances.
      """
      # check type
      for cb in cbs:
          assert isinstance(cb, Callback), cb.__class__
      self.cbs = cbs
  
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 1 to create a new Callbacks object from inherited base classes: Callback with example: obj = Callbacks(cbs)