Python: Shuffle not working in class initialiser

Question

I want to write a class "SomeClass" that stores a shuffled version of the list it is initialised with. However, the list is shuffled in exactly the same way for every instance of my class. Could you please tell me what I am doing wrong?

import random


class SomeClass:

    def __init__(self, list):
        self.shuffled_list =list
        random.shuffle(self.shuffled_list)


list = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
A = SomeClass(list)
B = SomeClass(list)

# Why are both lists the same?
print(A.shuffled_list)
print('\n\n')
print(B.shuffled_list)

Dont use list as a variable name, it's python built-in type, for further information stackoverflow.com/questions/14694559/…. — Eden Refael
– Eden Refael, Commented Apr 4, 2024 at 23:03

Cory Kramer · Accepted Answer · 2024-04-04 22:52:09Z

2

All instances of your class will share the same list object, you need to copy it. Also don't use list as a variable name since you're shadowing the type

def __init__(self, values):
    self.shuffled_list = values.copy()
    random.shuffle(self.shuffled_list)

answered Apr 4, 2024 at 22:52

Cory Kramer

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1 Comment

ShadowRanger Over a year ago

I would slightly prefer self.shuffled_list = list(values). Calling .copy() will copy any old thing that happens to have that method, and you won't establish the invariant that you always store a list (and might get confusing errors from random.shuffle). self.shuffled_list = list(values) means the caller can pass a tuple or some other arbitrary iterable, and you'll handle it all the same, by shallow-copying to a new list.

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