python中使用yaml，PyYAML和ruamel.yaml简介

yaml格式基础

yaml格式的基础介绍在网上很多，可以参考下面这篇博客

https://www.jianshu.com/p/97222440cd08

总结一下yaml格式主要由3种格式组成 常量 对象 数组，用法见下面的例子

#即表示url属性值；
url: http://www.wolfcode.cn 
#即表示server.host属性的值；
server:
    host: http://www.wolfcode.cn 
#数组，即表示server为[a,b,c]
server:
    - 120.168.117.21
    - 120.168.117.22
    - 120.168.117.23
#常量
pi: 3.14   #定义一个数值3.14
hasChild: true  #定义一个boolean值
name: '你好YAML'   #定义一个字符串

用python读写yaml

python中读写yaml存在两个包，自带的PyYAML包和ruamel.yaml包，ruamel.yaml包在PyYAML包上进行了一些改进，下面分别介绍如何使用这两个包

PyYAML

PyYAML的官方APi文档[https://pyyaml.org/wiki/PyYAMLDocumentation]
其中最常用的几个API如下

1. 读取一个yaml文件，yaml.load

yaml.load("""
... - Hesperiidae
... - Papilionidae
... - Apatelodidae
... - Epiplemidae
... """)

['Hesperiidae', 'Papilionidae', 'Apatelodidae', 'Epiplemidae']

 with open(r'test.yaml', 'r') as f:
    yaml.load(f)

yaml.load 可以解析字符串中的或者一个字符流对象中的yaml格式，把yaml中的数组解析成python的列表，常量和对象解析成python的字典，并支持嵌套的字典和列表
2. 读取多个文档中的yaml，yaml.load_all

>>> documents = """
... ---
... name: The Set of Gauntlets 'Pauraegen'
... description: >
...     A set of handgear with sparks that crackle
...     across its knuckleguards.
... ---
... name: The Set of Gauntlets 'Paurnen'
... description: >
...   A set of gauntlets that gives off a foul,
...   acrid odour yet remains untarnished.
... ---
... name: The Set of Gauntlets 'Paurnimmen'
... description: >
...   A set of handgear, freezing with unnatural cold.
... """

>>> for data in yaml.load_all(documents):
...     print data

{'description': 'A set of handgear with sparks that crackle across its knuckleguards.\n',
'name': "The Set of Gauntlets 'Pauraegen'"}
{'description': 'A set of gauntlets that gives off a foul, acrid odour yet remains untarnished.\n',
'name': "The Set of Gauntlets 'Paurnen'"}
{'description': 'A set of handgear, freezing with unnatural cold.\n',
'name': "The Set of Gauntlets 'Paurnimmen'"}

符号 — 用来定义同一个yaml流中的不同的文件档，用yaml.load_all可以分别读取yaml流中不同的文档，同理可以使用yaml.dump_all

>>> print yaml.dump_all([1,2,3], explicit_start=True)
--- 1
--- 2
--- 3

3. 把python对象转换为yaml格式的字符串，yaml.dump

>>> print yaml.dump({'name': 'Silenthand Olleander', 'race': 'Human',
... 'traits': ['ONE_HAND', 'ONE_EYE']})

name: Silenthand Olleander
race: Human
traits: [ONE_HAND, ONE_EYE]

desired_caps = {'name': 'Silenthand Olleander', 'race': 'Human','traits': ['ONE_HAND', 'ONE_EYE']}
with open(yamlpath, "w", encoding="utf-8") as f:
    yaml.dump(desired_caps, f)

yaml.dump接受一个python对象，并解析成一个yaml格式的字符串，并且可以由第二个参数指定要输出的文件。但是yaml.dump不能很好的处理嵌套的字典，下面的例子中嵌套的字典被解析为｛｝

print(yaml.dump({ 'chromeOptions': {'androidProcess': 'com.tencent.mm:tools'}}))

chromeOptions: {androidProcess: 'com.tencent.mm:tools'}

用ruamel.yaml读写yaml

ruamel.yaml的API文档[https://yaml.readthedocs.io/en/latest/overview.html]
ruamel.yaml的用法和PyYAML基本一样，并且默认支持更新的YAML1.2版本

1. 读取yaml文件

from ruamel.yaml import YAML

yaml=YAML(typ='safe')   # default, if not specfied, is 'rt' (round-trip)
yaml.load(doc)

在这doc可以是一个文件指针（即具有 .read()方法，字符串或一个 pathlib.Path())。typ='safe’的作用是：加载文档而不解析未知标记
2. python对象转换成yaml流

from ruamel.yaml import YAML

yaml=YAML()
yaml.default_flow_style = False
yaml.dump({'a': [1, 2]}, s)

在这s可以是文件指针（即具有.write()方法的对象 ，或者pathlib.Path())
3. 旧的ruamel.yaml API

import ruamel.yaml
ruamel.yaml.load(doc, ruamel.yaml.RoundTripLoader)
ruamel.yaml.dump(code, s, Dumper=ruamel.yaml.RoundTripDumper)

4. 更多的例子

import sys
from ruamel.yaml import YAML

inp = """\
# example
name:
  # details
  family: Smith   # very common
  given: Alice    # one of the siblings
"""

yaml = YAML()
code = yaml.load(inp)
code['name']['given'] = 'Bob'

yaml.dump(code, sys.stdout)

输出

# example
name:
  # details
  family: Smith   # very common
  given: Bob      # one of the siblings