class_docstr: Basic in-memory dict-based object for saving Task Records.
  
  This is the first object to present the DB interface
  for logging tasks out of memory.
  
  The interface is based on MongoDB, so adding a MongoDB
  backend should be straightforward.
docstr: get all msg_ids, ordered by time submitted.
docstr_tok: ["get","all","msg_ids",",","ordered","by","time","submitted","."]
code: def get_history(self):
      """get all msg_ids, ordered by time submitted."""
      msg_ids = self._records.keys()
      # Remove any that do not have a submitted timestamp.
      # This is extremely unlikely to happen,
      # but it seems to come up in some tests on VMs.
      msg_ids = [
          m
          for m in msg_ids
          if self._records[m]["submitted"] is not None
      ]
      return sorted(
          msg_ids, key=lambda m: self._records[m]["submitted"]
      )
  
imports: import copy
  from copy import deepcopy
  from datetime import datetime
  from traitlets import Dict, Float, Integer, Unicode
  from traitlets.config.configurable import LoggingConfigurable
  from ..util import ensure_timezone
label_desc: Use image node_id 15 for calling the DictDB obj's underlying member method code with example usage: obj.get_history() and returns: sorted