code: def get_node(self, value):
          
          while True:
              self.cursor.execute(
                  'SELECT id FROM nodes WHERE value=?',
                  (value,)
              )
              node = self.cursor.fetchone()
              if node is not None:
                  return node[0]
              self.cursor.execute(
                  'INSERT INTO nodes (value) VALUES (?)',
                  (value,)
              )
docs: Get node ID by value.
  
          If a node with the specified value does not exist,
          create it and return its ID.
  
          Parameters
          ----------
          value : `str`
              Node value.
  
          Returns
          -------
          `int`
              Node ID.