code: def set_ctx(self, ctx):
          
          todo = deque([self])
          while todo:
              node = todo.popleft()
              if 'ctx' in node.fields:
                  node.ctx = ctx
              todo.extend(node.iter_child_nodes())
          return self
docs: Reset the context of a node and all child nodes.  Per default the
          parser will all generate nodes that have a 'load' context as it's the
          most common one.  This method is used in the parser to set assignment
          targets and other nodes to a store context.