Неправильный вывод после создания наследующиего класса

import  random,copy
 
class mat():
    s=[]
    s1=[]
    multistring=[]
    multistring1=[]
    def __init__ (self):
        for i in range(4):
            self.s.append([])
            for j in range(4):
                   self.s[i].append(random.randint(0,15))
        self.s1=copy.copy(self.s)
    
    def __del__(self):
         print('Dist')
         
    def matshow (self):
         print('\n'.join(map(str,self.s)))   
    
    def triangle (self):
        if self.s[0][1] == 0 and self.s[0][2] == 0 and self.s[1][2] == 0 or self.s[1][0] == 0 and self.s[2][0] == 0 and self.s[2][1] == 0:
            print ' It is triangle matrix'
        else:
            print 'It is not triangle matrix' 
 
    def diagonal (self):
        if self.s[0][1] == 0 and self.s[0][2] == 0 and self.s[1][2] == 0 and self.s[1][0] == 0 and self.s[2][0] == 0 and self.s[2][1] == 0:
            print 'It is diagonal matrix'
        else:
            print 'It is not diagonal matrix' 
 
    def multitask(self):
        for i in range(4):
            self.multistring.append([])
            for j in range(4):
                self.multistring[i].append([self.s[i][j]-self.s1[i][j]])
        return self.multistring     
a=mat() 
 
class mat1(mat):
    def multitask(self):
        zip(*self.s1)
        return self.s1
        
a1=mat1()

import copy
import random
 
 
class MathParent():
    s = []
    s1 = []
    multistring = []
    multistring1 = []
 
    def __init__(self):
        for i in range(4):
            self.s.append([])
            for j in range(4):
                self.s[i].append(random.randint(0, 15))
        self.s1 = copy.copy(self.s)
 
    def __del__(self):
        print('Dist')
 
    def matshow(self):
        print('\n'.join(map(str, self.s)))
 
    def triangle(self):
        if self.s[0][1] == 0 and self.s[0][2] == 0 and self.s[1][2] == 0 or self.s[1][0] == 0 and self.s[2][0] == 0 and self.s[2][1] == 0:
            print(' It is triangle matrix')
        else:
            print('It is not triangle matrix')
 
    def diagonal(self):
        if self.s[0][1] == 0 and self.s[0][2] == 0 and self.s[1][2] == 0 and self.s[1][0] == 0 and self.s[2][0] == 0 and self.s[2][1] == 0:
            print('It is diagonal matrix')
        else:
            print('It is not diagonal matrix')
 
    def multitask(self):
        for i in range(4):
            self.multistring.append([])
            for j in range(4):
                self.multistring[i].append([self.s[i][j] - self.s1[i][j]])
        return self.multistring
 
 
class MathChild(MathParent):
    def __init__(self):
        super(MathParent, self).__init__()
 
    def multitask(self):
        return zip(*self.s1)
 
a = MathParent()
a1 = MathChild()