Bummer! Got the wrong length for a `Hand`, Please if somebody could shed some light here.

Question

I am clearly passing two arguments in cls -> size and class, I have initialize the hand class to accept two arguments as well, what I am missing here any clue.

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

class D20(Die):
    def __init__(self):
        super().__init__(sides=20)

hands.py

from dice import D20


class Hand(list):
    def __init__(self, size=0, die_class=None, *args, **kwargs):
        #self.size=size
        for _ in range(size):
            self.append(die_class())
        super().__init__()

    @property
    def total(self):
        return sum(self)

    @classmethod
    def roll(cls, size):
        return cls(size=2, die_class=D20)

Answer 1 · 2017-07-05T03:10:15Z

July 5, 2017 3:10am

Hi there!

Ah, so close! Remember that python runs line by line, even inside methods inside classes! If you move your

super().__init__()

Above the for loop in your __init __ method, you won't get an empty Hand object anymore. What the super().__init __() line does is create the instance (self) using the __init _ _ method of the parent (list) class. If you run it last, you get a new instance of the list class with nothing in it, and that's the first reason you get the wrong length - the length will always be 0.

The second, is, I think just a typo or misunderstanding the question. In your classmethod roll,

def roll(cls, size):
        return cls(size=2, die_class=D20)

I think you got your default parameters backwards. Here roll() will expect one argument, but whatever it is, it will create a Hand instance of 2 D20 instances. You just need to remove the "=2" part, so the size can be set when calling the Hand.roll() method ( the checker will try sizes other than 2 as well) :)

A quick tip in the hope it helps:

In python 3, super() is so powerful, that we don't actually need to call super().__init __() if we're not passing in any values, we can literally just use super() as if we were calling the parent class with no arguments. For example:

class Array(list):  
    """A Friendly name for a list for new python users""" 
    def __init__(self,  itr):
        super()
        for _ in itr:
            self.append(_)

This gives us an Array instance with all the attributes and methods of a list, just a different name. However in this case, we're not really doing anything with that for loop, so here we could just use list's __init __ method. To pass in the itr value, we do need to use super().__init __() however (otherwise super would think we were giving it the itr value!):

class Array(list):  
    """A Friendly name for a list for new python users""" 
    def __init__(self, itr):
        super().__init__(itr)

And again, Array instances have all the qualities of lists :)

Hope it helps!

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shekhar bhardwaj

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Bummer! Got the wrong length for a `Hand`, Please if somebody could shed some light here.

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Jon Mirow