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Python Object-Oriented Python Advanced Objects Frustration

Shawn Zhu
Shawn Zhu
3,884 Points

Got stuck on a challenge task, please help.

Hey guys, can someone point out whats wrong with my code? Every time I press the recheck work button, it says:

TypeError: init() missing 1 required positional argument: 'alist'

I got frustrated so I copy and pasted my code into workspace, in the console I assigned a = [1, 2, 3, 4, 5] and put in len(Liar(a)), it will return 8 or 2 like the task asked me to do. But in the challenge window it alway shows an error, can anyone point out what`s wrong with my code or did I misunderstand the task? Thank you so much.

frustration.py
import random

class Liar(list):
    def __init__(self, alist):
        self.alist = alist

    def __len__(self):
        b = random.uniform(0, 4)
        if b > 2:
            return len(self.alist) + 3
        elif b < 2:
            return len(self.alist) - 3
Shawn Zhu
Shawn Zhu
3,884 Points

Here is the task:

Now I want you to make a subclass of list. Name it Liar.

Override the len method so that it always returns the wrong number of items in the list. For example, if a list has 5 members, the Liar class might say it has 8 or 2.

You'll probably need super() for this.

1 Answer

Jeff Muday
MOD
Jeff Muday
Treehouse Moderator 26,998 Points

I like how you are approaching this challenge-- let's build on that.

There are so many ways that the challenge can be done correctly, but you're overthinking it somewhat. Because we are inheriting from list most of the work has been done for us! (I like the sound of that)

We don't have to put in an __init__() with a separate self.alist since we are already have storage we inherited from the list() class.

We only need to override the dunder len method __len()__ see below.

Good luck with Python, object orientation is something you will use all the time!

import random
class Liar(list):
    def __len__(self):
        # get length from superclass
        super_len = super().__len__()
        # liar_len can be any value that is not super_len
        # your idea of using a random addition is perfect
        liar_len = super_len + random.randint(1,4)
        # finally return our liar_len
        return liar_len
Shawn Zhu
Shawn Zhu
3,884 Points

Thank you for the help, good sir.