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Python Object-Oriented Python Advanced Objects Frustration

Jennifer Lithgow
Jennifer Lithgow
11,778 Points
Posted by Jennifer Lithgow
Jennifer Lithgow
11,778 Points

Frustration.py

I am super lost with this challenge. I can follow along with the examples in the preceeding video, but I have no idea how I could alter len to give a wrong number. I don't even know where to begin on this one. In IDLE, tried to even just set it up and put in "pass" just to see if I could get len to work WITHOUT altering it, and I couldn't get anything to run. "Frustration" is an appropriate name for this challenge. :(

frustration.py 
class Liar(list):
    def __len__(self):
        super().__len__()
        return self

10 Answers

Kenneth Love
STAFF
Kenneth Love
Treehouse Guest Teacher
Kenneth Love
Kenneth Love
Treehouse Guest Teacher

If you call super().__len__() (and assign it to a variable, of course), you'll get the length of self (well, the instance, but that's the name inside the method), using __len__ from the parent class (list). Using that value, you can change it so that it's wrong. Add 1, remove 1, multiply by 2, whatever. Then return that new value.

Jennifer Lithgow
Jennifer Lithgow
11,778 Points
Jennifer Lithgow
Jennifer Lithgow
11,778 Points

"and assign it to a variable, of course" ooooooohhhhh, okay. That seems so simple, now! I don't know why I wasn't able to wrap my head around that before. (Too many lectures in a row, maybe? Ha ha ha!) That's super helpful. I'll go back and give it another go. Thank you!

Sharla Kew
Sharla Kew
15,356 Points

Could you elaborate a bit on when you would choose to set super().whatever (or just the magic method in the case of immutable types) as a variable and when you wouldn't?

ex:

class WeirdList(list):
    def __len__(self):
        super().__len__()

vs

class WeirdList(list):
    def __len__(self):
        weirdlen = super().__len__()
Kenneth Love
Kenneth Love
Treehouse Guest Teacher
Kenneth Love
Kenneth Love
Treehouse Guest Teacher

Sharla Kew it all depends on what the method does.

class BaseClass:
    def set_name(self, name="Kenneth"):
        self.name = name

class ChildClass(BaseClass):
    def set_name(self):
        super().set_name()
        self.name = self.name.upper()

In this example, calling the super() version of the method changes the instance and doesn't return anything so it's still effective to use it.

With __len__, though, it doesn't set anything on the instance and it returns a value. That return value needs to go somewhere, so we put it into a variable.

Sharla Kew
Sharla Kew
15,356 Points

Kenneth Love Ok so -

Some methods, what they do is set a variable, so why would you set a variable equal to the setting of a variable? ex: the set_name() method in your example.

Other methods, what they do is return a value, and you gotta store that in a variable or it vanishes into the ether. ex: __len__()

Putting super() on the beginning of them made them seem spooky but they need to be treated like normal methods.

Nice. Thanks Kenneth!

Alexander Davison
Alexander Davison
65,469 Points
Alexander Davison
Alexander Davison
65,469 Points

You can just return 2. That worked for me.

Qasa Lee
Qasa Lee
18,916 Points
Qasa Lee
Qasa Lee
18,916 Points 
class Liar(list):
    def __len__(self):
        return super().__len__() + 1

Check this out, good luck !

Nicholas Lim
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Nicholas Lim
Python Development Techdegree Student 6,055 Points
Nicholas Lim
.a{fill-rule:evenodd;}techdegree
Nicholas Lim
Python Development Techdegree Student 6,055 Points

OK everybody here's the answer:

import random
import math

class Liar(list):
    def __init__(self, *arg):
        self.arg = []
    def __len__(self):
        super().__len__()
        randomNum = random.randint(2, 9)
        x = len(self.arg) + math.factorial(randomNum)
        return x
Nicholas Lim
.a{fill-rule:evenodd;}techdegree
Nicholas Lim
Python Development Techdegree Student 6,055 Points

When you paste that in it will be correct. So mark the differences between yours and mine. Hopefully this helps.

Jay Norris
Jay Norris
14,824 Points
Jay Norris
Jay Norris
14,824 Points

I'm still lost. Am I going in the wrong direction here?

def Liar(list):
    def __len__(self):
        length = super().__len__()
        lie = length * 2
        return lie
Kenneth Love
Kenneth Love
Treehouse Guest Teacher
Kenneth Love
Kenneth Love
Treehouse Guest Teacher

You're really close. First, how do you define a class?

Second, it needs to always return a wrong length. What length would your current version give if there wasn't anything in the list?

Cristian Romero
Cristian Romero
11,911 Points
Cristian Romero
Cristian Romero
11,911 Points

hmm even after adding class this still doesn't work?

Jay Norris
Jay Norris
14,824 Points
Jay Norris
Jay Norris
14,824 Points

That worked! I was never going to notice that "def"

Thank you!

Tomas Svojanovsky
Tomas Svojanovsky
26,680 Points
Tomas Svojanovsky
Tomas Svojanovsky
26,680 Points 
import random
from operator import add, sub


class Liar(list):
    def __len__(self):
        ops = (add, sub)
        op = random.choice(ops)
        length = super().__len__()

        return op(length, 3)
Nathan English
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Nathan English
Front End Web Development Techdegree Student 10,817 Points
Nathan English
.a{fill-rule:evenodd;}techdegree
Nathan English
Front End Web Development Techdegree Student 10,817 Points

This post is pretty old, but I'm just gonna leave this here. 

import random


class Liar(list):
    def __init__(self,*arg):
        self.arg = []
    def __len__(self):
        super().__len__()
        randomNum = random.randint(0,10)
        x = randomNum + len(self.arg)
        return x
Tapiwanashe Taurayi
Tapiwanashe Taurayi
15,889 Points
Tapiwanashe Taurayi
Tapiwanashe Taurayi
15,889 Points

import random import math

class Liar(list): def init(self, *arg): self.arg = [] def len(self): super().len() randomNum = random.randint(2, 9) x = len(self.arg) + math.factorial(randomNum) return x

sonny unverferth
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sonny unverferth
Python Web Development Techdegree Student 2,889 Points
sonny unverferth
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sonny unverferth
Python Web Development Techdegree Student 2,889 Points

Hey Ken, I have followed the python course from the beginning without skipping anything. Im stuck on this Challenge and have never seen _ _ len _ _ or .super() before. Its really frustrating. Any advice?

Temiye Oluseun
Temiye Oluseun
2,902 Points
Temiye Oluseun
Temiye Oluseun
2,902 Points

Hey try this class Liar(list): def len(self): length = super().len() wrong = 2 return wrong