class_docstr: Single global state to keep track of scope stacks.
code: def __init__(self):
      self._stack = []
  
imports: from collections import defaultdict
  from collections.abc import Iterable
  from functools import singledispatch
  import pyro
  from pyro.poutine.handlers import _make_handler
  from pyro.poutine.reentrant_messenger import ReentrantMessenger
  from pyro.poutine.runtime import effectful
label_desc: Use image node_id 1 to create a new ScopeStack object  with example: obj = ScopeStack()