code: def add_node(self, id, radius=8, style=style.DEFAULT, category="", label=None, root=False,
                   properties={}):
          
          
          
          if self.has_key(id): 
              return self[id]
              
          if not isinstance(style, str) and style.__dict__.has_key["name"]:
              style = style.name
          
          n = node(self, id, radius, style, category, label, properties)
          self[n.id] = n
          self.nodes.append(n)
          if root: self.root = n
              
          return n
docs: Add node from id and return the node object.