positional argument: 'self'

[menator01]

A link on self
The self parameter is a reference to the current instance of the class, and is used to access variables that belongs to the class.

Another example

#! /usr/bin/env python3

import random as rnd

word_list = ['a', 'random', 'list', 'of', 'words']

class Word:
    def __init__(self):
        self.my_list = None

    def get_word(self):
        word = rnd.choice(self.my_list)
        return word

word = Word() # Initiate class instant
word.my_list = word_list # Assign word list to instance variable
print(word.get_word()) # Print results of get word
print(word.get_word()) # Print another result

Output:
words
list