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Python Object-Oriented Python Dice Roller RPG Roller

Suraj Shah
Suraj Shah
1,055 Points
Posted by Suraj Shah
Suraj Shah
1,055 Points

Extending a class

I want my class D20 to extend class Die.

Please could you explain why this does not work:

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

How is it different from this (which works):

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

Thanks!

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, sides):
        super().__init__(sides = 20)
hands.py 
class Hand(list):
    @property
    def total(self):
        return sum(self)
Igor Ević
Igor Ević
5,827 Points

If you use only sides when you create class Die:

class Die:
    def __init__(self, sides=2):

you don't need sides in subclass init, because Die20 is special Die with sides = 20:

class Die20(Die):
    def __init__(self):
         super().__init__(sides=20)

When you define subclass D20 with:

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

you must provide sides when you create class Dice20

This works, but only if you create class with Die20() or Die20(20):

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

What if you call Die20(6)?

3 Answers

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,457 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,457 Points

The key is in the challenge text "It should automatically have 20 sides and shouldn't require any arguments to create.

# your first example says
class D20(Die):
    # __init__ takes one positional argument 'sides'
    def __init__(self, sides):
        # regardless of argument 'sides', 
        # call Die.__init__ with keyword argument set to 20
        super().__init__(sides = 20) # Note1
        # the positional argument 'sides' is not used

# Note1: here, the keyword 'sides' is only related to the parameter "sides" in the Die.__init__ parameter list. It has no relation to any local variable that might also be called "sides"

# your second example says:
class D20(Die):
    # __init__ takes one positional argument 'sides'
    # with default value 20
    def __init__(self, sides = 20):
        # call Die.__init__ with positional  argument set to argument value or the default 20
        super().__init__(sides)

Since the challenge checker doesn't provide the argument 'sides', the first one fails due to missing positional argument. The second one passes only because a default value is defined. The better answer removes sides parameter. 

class D20(Die):
    # __init__ takes no positional arguments
    def __init__(self):
        # call Die.__init__ with keyword argument set to 20
        super().__init__(sides = 20)

Post back if you need more help. Good luck!!!

Ngonidzaishe Tukuta
Ngonidzaishe Tukuta
4,274 Points
Ngonidzaishe Tukuta
Ngonidzaishe Tukuta
4,274 Points

Thanks Chris Freeman