Реализация класса в Python 3.7

так?

class Class:
    def __init__(self, A):
        self.A = A
    
    def __str__(self):
        s = ''
        
        for row in self.A:
            for cell in row:
                s += f"{cell} "
            s += "\n"
        
        return s

print(Class([[1, 4], [2, 6]]))

Элементарно:

class C():

    A = [[1, 4], [2, 6]]
    
    s = ''
    
    for row in A:
        for cell in row:
            s += f'{cell} '
        s += '\n'
    print(s)

C()