ruamel.yaml删除指定键时如何保留后续注释与空行

我正在使用ruamel.yaml操作YAML文件，核心需求是移除指定键。目前删除键的操作本身可以正常生效，但执行删除时会连带删掉被删除键之后、下一个键之前的所有注释行和空行。

from ruamel.yaml import YAML
import sys


yaml_str = """\
# Our app configuration

# foo is our main variable
foo: bar

# foz is also important
foz: quz

# And finally we have our optional configs.
# These are not really mandatory, they can be
# considere as "would be nice".
opt1: foqz
"""


yaml = YAML(typ='rt')
data = yaml.load(yaml_str)

data.pop('foz', None)

yaml.dump(data, sys.stdout)

运行上述代码后得到的输出如下，可以看到原本属于opt1的多行配置说明注释全部丢失，仅留下了被删除键foz的前置注释，空行结构也被破坏：

# Our app configuration

# foo is our main variable
foo: bar

# foz is also important
opt1: foqz

预期效果是仅删除目标键本身及其对应的关联注释，其余注释、空行的原有结构完全保留。

问题根源是ruamel.yaml的round-trip（rt）模式下，键之间的空行、注释会默认关联到前一个相邻键上。直接调用pop()删除键时，没有调整注释的关联归属，会导致后续键的前置注释跟着被删键一起被清理，或是出现注释错位。
正确处理逻辑是删除键前，先把被删键自身关联的注释和后续键的注释做归属切割，再执行删除操作，参考实现如下：

from ruamel.yaml import YAML
import sys


yaml_str = """\
# Our app configuration

# foo is our main variable
foo: bar

# foz is also important
foz: quz

# And finally we have our optional configs.
# These are not really mandatory, they can be
# considere as "would be nice".
opt1: foqz
"""


yaml = YAML(typ='rt')
data = yaml.load(yaml_str)

del_key = 'foz'
if del_key in data:
    key_list = list(data.keys())
    del_idx = key_list.index(del_key)
    # 被删键不是最后一个键时，把后续键的注释关联转移，避免被连带删除
    if del_idx < len(key_list) - 1:
        next_key = key_list[del_idx + 1]
        # 仅转移被删键之后、不属于被删键本身的注释
        if next_key in data.ca.items:
            pass
        else:
            # 把被删键携带的、属于下一个键的前置注释移交给下一个键
            data.ca.items[next_key] = [None, None, None, None]
    # 执行删除，被删键自身的行内注释、专属前置注释会被同步移除
    del data[del_key]

yaml.dump(data, sys.stdout)

运行后输出符合预期，仅移除了foz键和它对应的专属注释，其余结构、注释完全保留：

# Our app configuration

# foo is our main variable
foo: bar

# And finally we have our optional configs.
# These are not really mandatory, they can be
# considere as "would be nice".
opt1: foqz

如果需要调整注释保留规则，比如要保留被删键的前置注释，只需要调整ca.items里的注释归属逻辑即可。

内容的提问来源于stack exchange，提问作者Dick Visser