This code is giving a runtime error(nzec). Can anyone help?

# input the number of test cases
num = int(input())

# make a list
lst = []

#repeat for num times
for i in range(num):
    #take a test case as input, it will be a string
    string = input()
    # convert the test cases into ints and append them into the lst
    lst.append((int(string[0]), int(string[2])))

# print the pattern
for i in lst:
    # this loop prints a line of the pattern
    for j in range(i[0]):
        if j%2 is 0:
            for k in range(i[1]):
                if k%2 is 0:
                    print('*', end='')
                else:
                    print('.', end='')
            print()
        else:
            for k in range(i[1]):
                if k%2 is 0:
                    print('.', end='')
                else:
                    print('*', end='')
            print()
    if not i is lst[len(lst) - 1]:
        print()