Pre-defining the constructor value to none..when not given

Question

I'm creating a Node class that takes some parameters. One is called next which I would like to be set as None by the constructor if no value is supplied.

class Node(object):
    def __init__(self, next,data):
        self.data = data
        self.next = next

def X(self):
    node = Node(next ,data)

How can I do that?

You can use a default value for it in function header `__init__(self,data,next=None)` — Mazdak, Aug 13 '15 at 10:19
Read up on default values [here](https://docs.python.org/2/tutorial/controlflow.html#default-argument-values). — SuperBiasedMan, Aug 13 '15 at 10:21
As an aside, what is the `Node.X` method for? It's not doing anything useful here. And by the way, it's not indented properly. — Cyphase, Aug 13 '15 at 10:23

score 2 · Answer 1 · answered Aug 13 '15 at 10:19

Swap the order of the parameters to __init__() and give next a default value.

class Node(object):
    def __init__(self, data, next=None):
        self.data = data
        self.next = next

    def X(self):
        node = Node(data)


node_a = Node('A')
node_b = Node('B', node_b)

score 1 · Answer 2 · answered Aug 13 '15 at 10:19

Swap your arguments, and give next a default:

class Node(object):
    def __init__(self, data, next=None):
        self.data = data
        self.next = next

then simply not pass in a next node when creating one:

def foo():
    node = Node(data)

or pass in another node as the second argument:

def bar():
    node = Node(data, some_other_node)

Pre-defining the constructor value to none..when not given

2 Answers2