如何控制 PyYAML 对我的数据使用哪种标量形式？

问题描述 投票：0回答：6

我有一个具有短字符串属性和长多行字符串属性的对象。我想将短字符串写为 YAML 带引号的标量，将多行字符串写为文字标量：

my_obj.short = "Hello"
my_obj.long = "Line1\nLine2\nLine3"

我希望 YAML 看起来像这样：

short: "Hello"
long: |
  Line1
  Line2
  Line3

如何指示 PyYAML 执行此操作？如果我调用 

yaml.dump(my_obj)
，它会产生类似字典的输出：

{long: 'line1

    line2

    line3

    ', short: Hello}

（不知道为什么 long 是这样的双倍行距......）

我可以指示 PyYAML 如何处理我的属性吗？我想影响顺序和风格。

python yaml pyyaml
6个回答
71
投票

爱上了@lbt 的方法，我得到了这个代码：

import yaml

def str_presenter(dumper, data):
  if len(data.splitlines()) > 1:  # check for multiline string
    return dumper.represent_scalar('tag:yaml.org,2002:str', data, style='|')
  return dumper.represent_scalar('tag:yaml.org,2002:str', data)

yaml.add_representer(str, str_presenter)

# to use with safe_dump:
yaml.representer.SafeRepresenter.add_representer(str, str_presenter)

它使每个多行字符串都是块文字。

我试图避免猴子修补部分。 完全归功于@lbt 和@J.F.Sebastian。

38
投票

基于 Python 中是否有支持将长字符串转储为块文字或折叠块的 yaml 库？

import yaml
from collections import OrderedDict

class quoted(str):
    pass

def quoted_presenter(dumper, data):
    return dumper.represent_scalar('tag:yaml.org,2002:str', data, style='"')
yaml.add_representer(quoted, quoted_presenter)

class literal(str):
    pass

def literal_presenter(dumper, data):
    return dumper.represent_scalar('tag:yaml.org,2002:str', data, style='|')
yaml.add_representer(literal, literal_presenter)

def ordered_dict_presenter(dumper, data):
    return dumper.represent_dict(data.items())
yaml.add_representer(OrderedDict, ordered_dict_presenter)

d = OrderedDict(short=quoted("Hello"), long=literal("Line1\nLine2\nLine3\n"))

print(yaml.dump(d))

输出

short: "Hello"
long: |
  Line1
  Line2
  Line3
15
投票

我希望任何带有 

\n
的输入都是块文字。使用 
yaml/representer.py
中的代码作为基础，我得到：

# -*- coding: utf-8 -*-
import yaml

def should_use_block(value):
    for c in u"\u000a\u000d\u001c\u001d\u001e\u0085\u2028\u2029":
        if c in value:
            return True
    return False

def my_represent_scalar(self, tag, value, style=None):
    if style is None:
        if should_use_block(value):
             style='|'
        else:
            style = self.default_style

    node = yaml.representer.ScalarNode(tag, value, style=style)
    if self.alias_key is not None:
        self.represented_objects[self.alias_key] = node
    return node


a={'short': "Hello", 'multiline': """Line1
Line2
Line3
""", 'multiline-unicode': u"""Lêne1
Lêne2
Lêne3
"""}

print(yaml.dump(a))
print(yaml.dump(a, allow_unicode=True))
yaml.representer.BaseRepresenter.represent_scalar = my_represent_scalar
print(yaml.dump(a))
print(yaml.dump(a, allow_unicode=True))

输出

{multiline: 'Line1

    Line2

    Line3

    ', multiline-unicode: "L\xEAne1\nL\xEAne2\nL\xEAne3\n", short: Hello}

{multiline: 'Line1

    Line2

    Line3

    ', multiline-unicode: 'Lêne1

    Lêne2

    Lêne3

    ', short: Hello}

After override

multiline: |
  Line1
  Line2
  Line3
multiline-unicode: "L\xEAne1\nL\xEAne2\nL\xEAne3\n"
short: Hello

multiline: |
  Line1
  Line2
  Line3
multiline-unicode: |
  Lêne1
  Lêne2
  Lêne3
short: Hello
8
投票

您可以使用 

ruamel.yaml
及其 RoundTripLoader/Dumper （免责声明：我是该包的作者）除了做您想做的事情之外，它还支持 YAML 1.2 规范（从 2009 年开始），并且有其他一些改进：

import sys
from ruamel.yaml import YAML

yaml_str = """\
short: "Hello"  # does keep the quotes, but need to tell the loader
long: |
  Line1
  Line2
  Line3
folded: >
  some like
  explicit folding
  of scalars
  for readability
"""

yaml = YAML()
yaml.preserve_quotes = True
data = yaml.load(yaml_str)
yaml.dump(data, sys.stdout)

给出：

short: "Hello"  # does keep the quotes, but need to tell the loader
long: |
  Line1
  Line2
  Line3
folded: >
  some like
  explicit folding
  of scalars
  for readability

（包括评论，与之前在同一列开始）

您也可以从头开始创建此输出，但随后您 确实需要提供额外的信息，例如折叠位置的明确位置。

5
投票

值得注意的是 pyyaml 不允许块标量中存在尾随空格，并将强制内容采用双引号格式。看来很多人都遇到过这个问题。如果您不关心能够往返数据，这将删除那些尾随空格：

def str_presenter(dumper, data):
    if len(data.splitlines()) > 1 or '\n' in data:  
        text_list = [line.rstrip() for line in data.splitlines()]
        fixed_data = "\n".join(text_list)
        return dumper.represent_scalar('tag:yaml.org,2002:str', fixed_data, style='|')
    return dumper.represent_scalar('tag:yaml.org,2002:str', data)

yaml.add_representer(str, str_presenter)
0
投票

使用 

ruamel.yaml
由 Anthon 在这里发布，这里有一些简单的函数可以将 yaml 文本转换为 dict，反之亦然，您可以方便地保留在实用程序函数中：

from ruamel.yaml import YAML
from io import StringIO

def yaml2dict(y):
    return YAML().load(y)

def dict2yaml(d):
    output_stream = StringIO()
    YAML().dump(d, output_stream)
    return output_stream.getvalue()

要听写的多行 yaml 示例：

y = """
title: organelles absent in animal cells and present in a plant cell
question: |
  Observe the following table and identify if the cell is of a plant or an animal
  | Organelle | Present/Absent | 
  |---------- | -------------- | 
  | Nucleus | Present |
  | Vacuole | Present |
  | Cellwall | Absent |
  | Cell membrane | Present |
  | Mitochondria | Present |
  | Chlorophyll | Absent |
answer_type: MCQ_single
choices:
- Plant
- Animal
points: 1
"""
d = yaml2dict(y)
d

输出：

{'title': 'organelles absent in animal cells and present in a plant cell', 'question': 'Observe the following table and identify if the cell is of a plant or an animal\n| Organelle | Present/Absent | \n|---------- | -------------- | \n| Nucleus | Present |\n| Vacuole | Present |\n| Cellwall | Absent |\n| Cell membrane | Present |\n| Mitochondria | Present |\n| Chlorophyll | Absent |\n', 'answer_type': 'MCQ_single', 'choices': ['Plant', 'Animal'], 'points': 1}

将其转换回 yaml：

y2 = dict2yaml(d)
print(y2)

输出：

title: organelles absent in animal cells and present in a plant cell
question: |
  Observe the following table and identify if the cell is of a plant or an animal
  | Organelle | Present/Absent | 
  |---------- | -------------- | 
  | Nucleus | Present |
  | Vacuole | Present |
  | Cellwall | Absent |
  | Cell membrane | Present |
  | Mitochondria | Present |
  | Chlorophyll | Absent |
answer_type: MCQ_single
choices:
- Plant
- Animal
points: 1

为了完整起见，请通过以下方式安装 

ruamel.yaml
：

pip install ruamel.yaml
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