First solution I submitted was:

    N, M = map(int,input().split())
    for i in range(1,N,2):
        print(('.|.'*i).center(M,'-'))
    print('Welcome'.center(M,'-'))
    for i in range(N-2,0,-2):
        print(('.|.'*i).center(M,'-'))

Then I used list comprehension and my second solution was:

    N, M = map(int,input().split())
    pattern = [('.|.'*i).center(M,'-') for i in range(1,N,2)]
    print('\n'.join(pattern),'\n'+'WELCOME'.center(M,'-'),'\n'+'\n'.join(pattern[::-1]))

Almost identical to your solution but the print was a mess. I saw your comment here and stole that print statement (I don't know why I didn't think of creating one big list then using join to print it effectively, but I have learnt now.)