Python - class Matrix - (Stackoverflow)

# author: Bartlomiej "furas" Burek (https://blog.furas.pl)
# date: 2020.07.07
# https://stackoverflow.com/questions/62780283/why-am-i-getting-attributeerror-for-tuple-object
# Why am i getting AttributeError for tuple object? [closed]

class Matrix:

    def __init__(self, rows=0, columns=0):
        if rows == 0 and columns == 0:
            self.rows, self.columns = map(int, input().split())
        else:
            self.rows = rows
            self.columns = columns
        self.dimension = (self.rows, self.columns)

    def pack_matrix(self):
        self.value = tuple(tuple(int(i) for i in input().split()) for _ in range(self.rows))

    def __str__(self):
        string = ""
        for row in range(self.rows):
            for col in range(self.columns):
                string = string + str(self.value[row][col]) +" "
            string +="\n"
        return string.strip()

    def __add__(self, other):
        if self.rows == other.rows and self.columns == other.columns:
            new_matrix = Matrix(self.rows, self.columns)

            all_rows = []
            for row in range(self.rows):
                all_cols = []
                for col in range(self.columns):
                    all_cols.append(self.value[row][col] + other.value[row][col])
                all_cols = tuple(all_cols)
                all_rows.append(all_cols)
            all_rows = tuple(all_rows)

            #new_matrix.value = tuple(tuple(int(i) for i in row) for row in range(all_rows))

            new_matrix.value = all_rows

            return new_matrix
        else:
            return "ERROR"

# --- main ---

m = Matrix(1, 2)
m.value = ((1,2),)

n = Matrix(1, 2)
n.value = ((3,4),)

print( (m + n).value )