class_docstr: Manage background execution of callbacks with a celery queue.
class_docstr_tok: ["Manage","background","execution","of","callbacks","with","a","celery","queue","."]
code: def get_progress(self, key):
      progress_key = self._make_progress_key(key)
      progress_data = self.handle.backend.get(progress_key)
      if progress_data:
          self.handle.backend.delete(progress_key)
          return json.loads(progress_data)
  
      return None
  
imports: import json
  import traceback
  from contextvars import copy_context
  from _plotly_utils.utils import PlotlyJSONEncoder
  from dash._callback_context import context_value
  from dash._utils import AttributeDict
  from dash.exceptions import PreventUpdate
  from dash.long_callback.managers import BaseLongCallbackManager
label_desc: Use image node_id 9 for calling the CeleryManager obj's underlying member method code with example usage: obj.get_progress(key) and returns: None, json