nodes: 0, module; 1, function_definition; 2, function_name:add_node; 3, parameters; 4, block; 5, identifier:self; 6, identifier:node; 7, default_parameter; 8, expression_statement; 9, comment:# Check for networkx 2.0 syntax; 10, if_statement; 11, expression_statement; 12, identifier:weight; 13, None; 14, comment:"""
          Adds a single node to the Graph.
  
          Parameters
          ----------
          node: str, int, or any hashable python object.
              The node to add to the graph.
  
          weight: int, float
              The weight of the node.
  
          Examples
          --------
          >>> from pgmpy.base import DAG
          >>> G = DAG()
          >>> G.add_node(node='A')
          >>> sorted(G.nodes())
          ['A']
  
          Adding a node with some weight.
          >>> G.add_node(node='B', weight=0.3)
  
          The weight of these nodes can be accessed as:
          >>> G.node['B']
          {'weight': 0.3}
          >>> G.node['A']
          {'weight': None}
          """; 15, boolean_operator; 16, block; 17, else_clause; 18, call; 19, boolean_operator; 20, call; 21, expression_statement; 22, if_statement; 23, block; 24, attribute; 25, argument_list; 26, call; 27, comparison_operator:len(node) == 2; 28, identifier:isinstance; 29, argument_list; 30, assignment; 31, comparison_operator:attrs.get('weight', None) is not None; 32, block; 33, expression_statement; 34, call; 35, identifier:add_node; 36, identifier:node; 37, keyword_argument; 38, identifier:isinstance; 39, argument_list; 40, call; 41, integer:2; 42, subscript; 43, identifier:dict; 44, pattern_list; 45, identifier:node; 46, call; 47, None; 48, expression_statement; 49, assignment; 50, identifier:super; 51, argument_list; 52, identifier:weight; 53, identifier:weight; 54, identifier:node; 55, identifier:tuple; 56, identifier:len; 57, argument_list; 58, identifier:node; 59, integer:1; 60, identifier:node; 61, identifier:attrs; 62, attribute; 63, argument_list; 64, assignment; 65, identifier:attrs; 66, dictionary; 67, identifier:DAG; 68, identifier:self; 69, identifier:node; 70, identifier:attrs; 71, identifier:get; 72, string; 73, None; 74, subscript; 75, identifier:weight; 76, pair; 77, string_content:weight; 78, identifier:attrs; 79, string; 80, string; 81, identifier:weight; 82, string_content:weight; 83, string_content:weight
code: def add_node(self, node, weight=None):
          """
          Adds a single node to the Graph.
  
          Parameters
          ----------
          node: str, int, or any hashable python object.
              The node to add to the graph.
  
          weight: int, float
              The weight of the node.
  
          Examples
          --------
          >>> from pgmpy.base import DAG
          >>> G = DAG()
          >>> G.add_node(node='A')
          >>> sorted(G.nodes())
          ['A']
  
          Adding a node with some weight.
          >>> G.add_node(node='B', weight=0.3)
  
          The weight of these nodes can be accessed as:
          >>> G.node['B']
          {'weight': 0.3}
          >>> G.node['A']
          {'weight': None}
          """
  
          # Check for networkx 2.0 syntax
          if isinstance(node, tuple) and len(node) == 2 and isinstance(node[1], dict):
              node, attrs = node
              if attrs.get('weight', None) is not None:
                  attrs['weight'] = weight
          else:
              attrs = {'weight': weight}
  
          super(DAG, self).add_node(node, weight=weight)