code: def has_node_with_value(self, value):
          
          for node in self.node_list:
              if node.value == value:
                  return True
          else:
              return False
docs: Whether any node in ``self.node_list`` has the value ``value``.
  
          Args:
              value (Any): The value to find in ``self.node_list``
  
          Returns: bool
  
          Example:
              >>> from blur.markov.node import Node
              >>> node_1 = Node('One')
              >>> graph = Graph([node_1])
              >>> graph.has_node_with_value('One')
              True
              >>> graph.has_node_with_value('Foo')
              False