python node class

1class Node(object):
2 
3    def __init__(self, data=None, next_node=None):
4        self.data = data
5        self.next_node = next_node
6

1You need to find the last node without a .nextEl pointer and add the node there:
2
3def add(self, newNode):
4    node = self.firstNode
5    while node.nextEl is not None:
6        node = next.nextEl
7    node.nextEl = newNode
8Because this has to traverse the whole list, most linked-list implementations also keep a reference to the last element:
9
10class List(object):
11    first = last = None
12
13    def __init__(self, fnode):
14        self.add(fnode)
15
16    def add(self, newNode):
17        if self.first is None:
18            self.first = self.last = newNode
19        else:
20            self.last.nextEl = self.last = newNode
21Because Python assigns to multiple targets from left to right, self.last.nextEl is set to newNode before self.last.
22
23Some style notes on your code:
24
25Use is None and is not None to test if an identifier points to None (it's a singleton).
26There is no need for accessors in Python; just refer to the attributes directly.
27Unless this is Python 3, use new-style classes by inheriting from object:
28
29class Node(object):
30    # ...

1class Node:
2
3    def __init__(self, data):
4
5        self.left = None
6        self.right = None
7        self.data = data
8
9
10    def PrintTree(self):
11        print(self.data)
12
13root = Node(10)
14
15root.PrintTree()