def load_vertices(fname):
    with open(fname) as f:
        res = [
            map(float, s.split(' ')[1:])
            for s in f if s.startswith('v ')
        ]
    return np.array(res)

def save_vertices(fname, new_vertices):
    with open(fname) as f:
        lines = f.readlines()
    counter = 0
    with open(fname, 'w') as f:
        for s in lines:
            if not s.startswith('v '):
                f.write(s)
                f.write('\n')
                continue
            f.write('v {} {} {}\n'.format(new_vertices[counter]))
            counter += 1