样式和注解信息都通过特殊的属性附加到CommentedMap中。样式可以复制，但注解部分索引到它们出现的行的关键字，如果您转换该关键字，则还需要转换索引的注解。
在你的第一个例子中，你将f()应用于键和值，我将在我的例子中使用单独的函数，所有的键都是大写的，所有的值都是小写的（当然，这只适用于字符串类型的键和值，所以这是例子的限制，而不是解决方案的限制）

import sys
import ruamel.yaml
from ruamel.yaml.comments import CommentedMap as CM
from ruamel.yaml.comments import Format, Comment

yaml_str = """\
# example YAML document
abc: All Strings are Equal  # but some Strings are more Equal then others
klm: Flying Blue
xYz: the End                # for now
"""

def fkey(s):
    return s.upper()

def fval(s):
    return s.lower()

def transform(data, fk, fv):
    d = CM()
    if hasattr(data, Format.attrib):
        setattr(d, Format.attrib, getattr(data, Format.attrib))
    ca = None
    if hasattr(data, Comment.attrib):
        setattr(d, Comment.attrib, getattr(data, Comment.attrib))
        ca = getattr(d, Comment.attrib)
    # as the key mapping could map new keys on old keys, first gather everything
    key_com = {}
    for k in data:
        new_k = fk(k)
        d[new_k] = fv(data[k])
        if ca is not None and k in ca.items:
            key_com[new_k] = ca.items.pop(k)
    if ca is not None:
        assert len(ca.items) == 0
        ca._items = key_com  # the attribute, not the read-only property
    return d

yaml = ruamel.yaml.YAML()
data = yaml.load(yaml_str)

# the following will print any new CommentedMap with curly braces, this just here to check
# if the style attribute copying is working correctly, remove from real code
yaml.default_flow_style = True

data = transform(data, fkey, fval)
yaml.dump(data, sys.stdout)

其给出：

# example YAML document
ABC: all strings are equal  # but some Strings are more Equal then others
KLM: flying blue
XYZ: the end                # for now

请注意：

• 以上尝试（并且成功）在原始列中开始注解，如果这是不可能的，例如，当变换的键或值占用更多空间时，它被进一步推到右边。
• 如果你有一个更复杂的数据结构，递归地遍历树，向下遍历Map和序列。在这种情况下，存储(key, value, comment)元组比存储pop()所有键并重新插入存储的值（而不是重建树）可能更容易。