code: def no_instance_caching():
      
      # this assumes that no sub-class of Expression shadows
      # Expression.instance_caching
      orig_flag = Expression.instance_caching
      Expression.instance_caching = False
      try:
          yield
      finally:
          Expression.instance_caching = orig_flag
docs: Temporarily disable instance caching in :meth:`~.Expression.create`
  
      Within the managed context, :meth:`~.Expression.create` will not use any
      caching, for any class.