code: def __exit__(self, *args):
      for c in self.callbacks:
          RayDaskCallback.ray_active.discard(c)
  
imports: import contextlib
  from collections import namedtuple, defaultdict
  from datetime import datetime
  from dask.callbacks import Callback
label_desc: Use image node_id 3 for calling the add_ray_callbacks obj's underlying member method code with example usage: obj.__exit__() without return types