why am i getting nzec error and how to fix it? problem code:SUMTRIAN

import psyco
psyco.full()

class matrix:                         #class1
    def __init__(self,no_of_rows):
        self.no_of_rows=no_of_rows
        self.matrix=[]*(self.no_of_rows)
    def fill_matrix(self):
        for i in range(self.no_of_rows):
            row=input().split()
            for j in range(len(row)):
                row[j]=int(row[j])
            self.matrix.append(row)
class problem_solution(matrix):                 #class2
    def __init__(self,class1):
        self.no_of_rows=class1.no_of_rows
        self.matrix=class1.matrix
        self.table_matrix=[None]*(class1.no_of_rows+1)
        for i in range(class1.no_of_rows+1):
            self.table_matrix[i]=[None]*(class1.no_of_rows+1)
    def solve(self,i,j):
        if(self.table_matrix[i][j] != None):
            return self.table_matrix[i][j]
        elif i>self.no_of_rows:
            self.table_matrix[i][j]=0
            return 0
        else:
            try:
                sum1=self.solve(i+1,j)
                sum2=self.solve(i+1,j+1)
                sum3=self.matrix[i][j]+max(sum1,sum2)
                return sum3
            except:
                self.table_matrix[i][j]=0
                return 0
def main():
    test_cases=int(input())
    for i in range(test_cases):
        no_of_rows=int(input())
        new_matrix=matrix(no_of_rows)
        new_matrix.fill_matrix()
        solution=problem_solution(new_matrix)
        print(solution.solve(0,0))
if __name__=='__main__':
    main()
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