python 3.8 - IndexError: list index out of range. appending to list

Question

I created a class Matrix. I've been trying to fill this matrix by randomize method, But this error was shown:

self.data[i].append(value)
IndexError: list index out of range

full code:

import random
class Matrix:
    def __init__(self, rows, cols):
        self.rows=rows
        self.cols=cols
        self.data=[]
    def randomize(self):
        for i in range(self.rows):
            for j in range(self.cols):
                value=random.randint(0, 10)
                self.data[i].append(value)

question from:https://stackoverflow.com/questions/65953086/indexerror-list-index-out-of-range-appending-to-list

Answer 1

You need to initialize the self.data list before accessing it with self.data[i] in the randomize function. You can do this with:

self.data=[[] for x in range(rows)]