yoba = [(None, None), (None, 'Smack my Bitch Up'), ('The Prodigy', None), ('The Prodigy', 'Smack my Bitch Up')]

def xstr(s):
    return '' if s is None else str(s)

def dologic(A, B):
    if (A and not B) or (not A and B):
        return xstr(A) + xstr(B)
    elif (A and B):
        return str(A) + ' - ' + str(B)
    else:
        return '...'
        
for A, B in yoba:
    print(dologic(A, B))