code: def ref(self, name):
      rv = self.find_ref(name)
      if rv is None:
          raise AssertionError(
              "Tried to resolve a name to a reference that "
              "was unknown to the frame (%r)" % name
          )
      return rv
  
imports: from ._compat import iteritems
  from .visitor import NodeVisitor
label_desc: Use image node_id 6 for calling the Symbols obj's underlying member method code with example usage: obj.ref(name) and returns: rv