Python Subclass Attribute Error

Question

During a lecture today we began to do work with subclasses within Python. As an example, we were given code resembling a very basic social network which is as follows:

class socialNetwork:
    class node:
        def __init__(self, name, friendList):
            self.name=name
            self.friendList=friendList

        def __init__(self):
            self.nodeList=[]

        def addPerson(self, name, friendList):
            person=self.node(name,friendList)
            self.nodeList.append(person)

s = socialNetwork()
s.addPerson("John",["Alice","Bob"])
s.addPerson("Alice",["John","Bob","Jeff"])
s.addPerson("Bob",["John","Alice","Jeff","Ken"])
s.addPerson("Jeff",["Alice","Bob","Barbra"])
s.addPerson("Ken",["Bob","Barbra"])
s.addPerson("Barbra",["Jeff","Ken"])
for person in s.nodeList:
    print("name: ",person.name, "\n\t friends: ",person.friendList)

However, whenever I attempt to run this, I receive the following message:

Traceback (most recent call last):
** IDLE Internal Exception: 
  File "C:\Users\Mike\AppData\Local\Programs\Python\Python36-
32\lib\idlelib\run.py", line 460, in runcode
    exec(code, self.locals)
  File "C:/Users/Mike/AppData/Local/Programs/Python/Python36-32/run.py", 
line 15, in <module>
    s.addPerson("John",["Alice","Bob"])
AttributeError: 'socialNetwork' object has no attribute 'addPerson'

Simply put, I have no idea why I am encountering this error, especially after the professor ran the same code just fine. Am I missing something here, and if so could someone please point it out?

Answer 1

You haven't defined any subclasses. Inheritance is specified in Python by putting the parent class(es) in parenthesis, e.g.:

class Node:
    pass

class Leaf(Node):
    # Leaf is a subclass of Node
    pass

"Network" and "Node" don't really make sense to be subclasses, but one should be composed of the other.

What you've done is define a class socialNetwork with one attribute, a class called node. That's why you get an AttributeError, because there is no addPerson attribute in socialNetwork.

Answer 2

Your class doesn't have addPerson method, because your class is indented wrong way. It should look like this:

class socialNetwork:
    class node:
        def __init__(self, name, friendList):
            self.name=name
            self.friendList=friendList

    def __init__(self):
        self.nodeList=[]

    def addPerson(self, name, friendList):
        person=self.node(name,friendList)
        self.nodeList.append(person)

Indentation does matter in python. A clue that something is wrong would be you having two __init__ methods at the same level.

Answer 3

Firstly, node is not a subclass of socialNetwork but a class nested within the latter. Secondly, socialNetwork actually has no attribute addPerson, but socialNetwork.node does.