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Python Object-Oriented Python Dice Roller RPG Roller

Code works on workspaces but getting "Can't get the length of a 'Hand'" error

For the rpg-roller code challenge, I am getting the error "Can't get the length of a 'Hand'". However when I run the same code in workspaces I do get the correct value for len(h).

My implementation is

from dice import D20

class Hand(list):
    @property
    def total(self):
        return sum(self)

    def __init__(self):
        super().__init__()

    def roll(self, size):
        for _ in range(size):
            self.append(D20())

When I run this

>>> import hands
>>> h = hands.Hand()
>>> h
[]
>>> h.roll(2)
>>> h
[15, 7]
>>> len(h)
2
>>> h.total
22

This seems to be what the challenge is asking for. What am I missing from my implementation?

dice.py
import random


class Die:
    def __init__(self, sides=2):
        if sides < 2:
            raise ValueError("Can't have fewer than two sides")
        self.sides = sides
        self.value = random.randint(1, sides)

    def __int__(self):
        return self.value

    def __add__(self, other):
        return int(self) + other

    def __radd__(self, other):
        return self + other

    def __repr__(self):
        return str(self.value)

class D20(Die):
    def __init__(self):
        super().__init__(sides=20)
hands.py
from dice import D20

class Hand(list):
    @property
    def total(self):
        return sum(self)

    def __init__(self):
        super().__init__()

    def roll(self, size):
        for _ in range(size):
            self.append(D20())

[MOD: added ```python formatting -cf]

3 Answers

Thanks, Steven- your answer was helpful!
Min, I pretty much did the same thing as you... checked it and it worked outside of the exercise... couldn't figure out what was going on till after I read this and played around with it ALOT... thanks for posting the question. My solution FINALLY passed after I made roll() into a class method that created an instance of Hand(), did the append() with D20() to this instance, and returned the instance.

I guess the clue that I should have used a class method is the "Hand.roll..." in the question. Totally missed that- I just thought that 'Hand' was a placeholder for a Hand instance. I assumed that the check would do something like:

h = Hand()
h.roll(2)
[etc.]

instead of.....

Hand.roll(2)
[etc.]

A hint to use a class method in the instructions could be really helpful! FYI Chris Freeman in case you deem it a worthy revision. Thanks, D.

Chris Freeman
Chris Freeman
Treehouse Moderator 68,457 Points

A @classmethod isn't explicitly required. A @staticmethod that doesn't use cls or self as its first parameter would also work.

A solution could have Hand.__init__ take a count argument for how many D20 die to initiate. Then have a static method roll pass the count value to the init and return Hand(count=count).

ds1, feel free to also tag Kenneth Love directly when you have a suggestion to improve a challenge.

Steven Parker
Steven Parker
231,275 Points

:warning: Be careful about testing a challenge in an external REPL.

If you have misunderstood the challenge, it's also very likely that you will misinterpret the results.

In this case, the challenge is expecting roll to return an instance of Hand, but your method doesn't return anything.

Another hint: since you're creating a new instance inside the method, this might be a good use for a classmethod or a "staticmethod".

Oh, Ok.. thanks for your help, Chris!