code: def add_node(self, node):
      if node in self:
          # If node already exists in the graph, return silently.
          return
      # Edge data is stored in dict value as a set.
      # Currently, it is used to store the DataPlaceholder(s) associated with the (multi)edge.
      self._successors[node] = defaultdict(set)
      self._predecessors[node] = defaultdict(set)
  
file_path: baikal/baikal/_core/digraph.py
imports: from collections import deque, defaultdict, OrderedDict
label_desc: Use image node_id 2 for calling the DiGraph obj's underlying member method code with example usage: obj.add_node(node) without return types