您的输出在Pagargaph 的值中没有换行符，因为您需要有一个block-style literal scalar（破折号修剪最后的换行符，您通常会在加载这样的标量时得到）：
Pagargaph: |-
Lorem ipsum dolor sit amet,
consectetur adipiscing elit,
sed do eiusmod tempor incididunt
ut labore et dolore magna aliqua.
你应该使用ruamel.yaml（免责声明：我是那个包的作者），它是专门为支持这种往返而开发的。得到你想做的事，例如：
import sys
import ruamel.yaml
from ruamel.yaml.scalarstring import PreservedScalarString as L
yaml_str = """\
ToGoFirst: aaa
Second: 'bbb' # insert after this one
Integer: 25
"""
yaml = ruamel.yaml.YAML()
yaml.preserve_quotes = True
d = yaml.load(yaml_str)
# yaml.indent(mapping=4, sequence=4, offset=2)
try:
before_integer = [k for k in d].index('Integer')
except ValueError:
before_integer = len(d)
d.insert(before_integer, 'Pagargaph', L('''Lorem ipsum dolor sit amet,
consectetur adipiscing elit,
sed do eiusmod tempor incididunt
ut labore et dolore magna aliqua.'''))
d.insert(before_integer, 'Something', 'extra', comment='with a comment')
yaml.dump(d, sys.stdout)
导致：
ToGoFirst: aaa
Second: 'bbb' # insert after this one
Something: extra # with a comment
Pagargaph: |-
Lorem ipsum dolor sit amet,
consectetur adipiscing elit,
sed do eiusmod tempor incididunt
ut labore et dolore magna aliqua.
Integer: 25
请注意：
- 在 ruamel.yaml (2.7, 3.4+) 支持的任何 Python 版本中都会保留该顺序
- 评论被保留
- 我在
bbb 周围添加的引号仅在您指定yaml.preserve_quotes = True 时才会保留
- 由于我们在位置 2 插入两次，后者将前者撞到位置 3。
您的用户必须有一定的纪律性，他们才能编辑 YAML 文件而不破坏它。他们还应该知道一些注意事项，例如普通（非引号）标量，不能以某些特殊字符开头或包含特殊字符序列（: 后跟空格，# 前面是空格）
为了帮助您的用户避免编辑错误，您可以尝试在 YAML 文档的开头添加以下注释：
# please read the first few "rules" of How_to_edit at the bottom of this file
最后：
How_to_edit: |
Editing a YAML document is easy, but there are some rules to keep you from
accidently invoking its hidden powers. Of the following you need at least
read and apply the ones up to the divider separating the important from less
important rules. The less important ones are interesting, but you probably
won't need to know them.
1) Entries in this file consist of a scalar key (before the ':') and a scalar
value (normally after the ':', but read rule 3).
2) Scalars do NOT need quotes (single: ', or double: ") around them, unless
you have a special character or characters combinations at the beginning
('%', '*', '&', '{', '[', '- ') or in the middle (': ', ' #) of the scalar.
If you add quotes use a single quote before and after the scalar . If
these are superfluous the program can remove them. So when in doubt just
add them.
3) A key followed by ': |' introduces a multiline scalar. These instructions
are in a multiline scalar. Such a scalar starts on the next line after ': |'.
The lines need to be indented, until the end of the scalar and these
indentation spaces are not part of the scalar.
The newlines in a multiline sclar are hard (i.e. preserved, and not
substituted with spaces).
If you see `: |-` that means the scalar is loaded with the trailing newline
stripped.
4) Anything after a space followed by a hash (' #') is a comment, when not
within quotes or in a multiline string.
--- end of the important rules ---
5) Within single quoted scalars you can have a single quote by doubling it:
rule 4: 'you probably don''t ever need that'
This is called escaping the single quote. You can double quote scalars, but
the rules for escaping are much more difficult, so don't try that at home.
6) The scalars consisting solely of "True" and "False" (also all-caps and
all-lowercase) are loaded as booleans when unquoted, and as strings when
quoted.
7) Scalars consisting solely of number characters (0-9) are loaded as numbers.
If there is a non-number they are usually loaded as strings, but scalars
starting with '0x' and '0o' and for the rest have only number characters,
are special and need quotes if not intended as (hexadecimal resp. octal)
numbers.
如果包含上述内容，您可能不想在往返时保留引号。