在您的with块中，您可以将所需的任何内容写入文件.由于您只需要在顶部添加评论，因此在调用ruamel之前先添加f.write()呼叫:

Within your with block, you can write anything you want to the file. Since you just need a comment at the top, add a call to f.write() before you call ruamel:

with open('test.yml', "w") as f:
    f.write('# Data for Class A\n')
    ruamel.yaml.dump(
        d, f, Dumper=ruamel.yaml.RoundTripDumper,
        default_flow_style=False, width=50, indent=8)