docstr: Instantiate a SqlObserver with an existing engine and session.
docstr_tok: ["Instantiate","a","SqlObserver","with","an","existing","engine","and","session","."]
code: def create_from(cls, engine, session, priority=DEFAULT_SQL_PRIORITY):
      """Instantiate a SqlObserver with an existing engine and session."""
      self = cls.__new__(cls)  # skip __init__ call
      self.engine = engine
      self.session = session
      self.priority = priority
      self.run = None
      self.lock = Lock()
      return self
  
imports: import json
  from threading import Lock
  import warnings
  from sacred.commandline_options import cli_option
  from sacred.observers.base import RunObserver
  from sacred.serializer import flatten
label_desc: Use image node_id 3 for calling the SqlObserver obj's underlying member method code with example usage: obj.create_from(cls, engine, session, priority) and returns: self