我想获得PyYAML的加载器加载映射（和有序映射）到Python 2.7+ OrderedDict类型，而不是香草dict，它目前使用对的列表。
什么是做到这一点的最好方法是什么？
更新：Python中3.6+你也许并不需要OrderedDict根本原因在于一直在使用的pypy一段时间（虽然被认为CPython的执行细节现在）的new dict implementation。
更新：在蟒蛇3.7+，字典对象的插入顺序保存性质已被宣布为Python语言规范的正式组成部分，见What's New In Python 3.7。
我喜欢@詹姆斯它的简单solution。然而，它改变默认的全局yaml.Loader类，这可能会导致麻烦的副作用。特别是，编写库代码时，这是一个坏主意。此外，它不直接与yaml.safe_load()工作。
幸运的是，该解决方案可以不费力地改进：
import yaml
from collections import OrderedDict
def ordered_load(stream, Loader=yaml.Loader, object_pairs_hook=OrderedDict):
class OrderedLoader(Loader):
pass
def construct_mapping(loader, node):
loader.flatten_mapping(node)
return object_pairs_hook(loader.construct_pairs(node))
OrderedLoader.add_constructor(
yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG,
construct_mapping)
return yaml.load(stream, OrderedLoader)
# usage example:
ordered_load(stream, yaml.SafeLoader)
对于序列化，我不知道一个明显的概括，但至少这应该不会有任何的副作用：
def ordered_dump(data, stream=None, Dumper=yaml.Dumper, **kwds):
class OrderedDumper(Dumper):
pass
def _dict_representer(dumper, data):
return dumper.represent_mapping(
yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG,
data.items())
OrderedDumper.add_representer(OrderedDict, _dict_representer)
return yaml.dump(data, stream, OrderedDumper, **kwds)
# usage:
ordered_dump(data, Dumper=yaml.SafeDumper)
YAML的模块，允许您指定自定义的“申述”转换Python对象为文本和“建设者”的逆过程。
_mapping_tag = yaml.resolver.BaseResolver.DEFAULT_MAPPING_TAG
def dict_representer(dumper, data):
return dumper.represent_dict(data.iteritems())
def dict_constructor(loader, node):
return collections.OrderedDict(loader.construct_pairs(node))
yaml.add_representer(collections.OrderedDict, dict_representer)
yaml.add_constructor(_mapping_tag, dict_constructor)
ruamel.yaml是替代PyYAML下降（免责声明：我是包的作者）。保存映射的顺序是在第一个版本（0.1）早在2015年加入它不仅保留你的字典顺序的事情之一，它也将保留意见，锚的名称，标签和不支持YAML 1.2规范（2009年发布）
该规范指出顺序不能保证，但当然也有在YAML文件排序及相应的解析器可以只坚持到和透明的产生，保持排序的对象。你只需要选择合适解析器，装载机和dumper¹：
import sys
from ruamel.yaml import YAML
yaml_str = """\
3: abc
conf:
10: def
3: gij # h is missing
more:
- what
- else
"""
yaml = YAML()
data = yaml.load(yaml_str)
data['conf'][10] = 'klm'
data['conf'][3] = 'jig'
yaml.dump(data, sys.stdout)
会给你：
3: abc
conf:
10: klm
3: jig # h is missing
more:
- what
- else
data的类型是CommentedMap其功能类似于字典，但具有围绕保持，直到被弃置的额外信息（包括保留意见！）
注意：有一个图书馆，基于以下的答案，这也实现了CLoader和CDumpers：Phynix/yamlloader
我很怀疑，这是做到这一点的最好办法，但是这是我想出的方式，它的工作。也可as a gist。
import yaml
import yaml.constructor
try:
# included in standard lib from Python 2.7
from collections import OrderedDict
except ImportError:
# try importing the backported drop-in replacement
# it's available on PyPI
from ordereddict import OrderedDict
class OrderedDictYAMLLoader(yaml.Loader):
"""
A YAML loader that loads mappings into ordered dictionaries.
"""
def __init__(self, *args, **kwargs):
yaml.Loader.__init__(self, *args, **kwargs)
self.add_constructor(u'tag:yaml.org,2002:map', type(self).construct_yaml_map)
self.add_constructor(u'tag:yaml.org,2002:omap', type(self).construct_yaml_map)
def construct_yaml_map(self, node):
data = OrderedDict()
yield data
value = self.construct_mapping(node)
data.update(value)
def construct_mapping(self, node, deep=False):
if isinstance(node, yaml.MappingNode):
self.flatten_mapping(node)
else:
raise yaml.constructor.ConstructorError(None, None,
'expected a mapping node, but found %s' % node.id, node.start_mark)
mapping = OrderedDict()
for key_node, value_node in node.value:
key = self.construct_object(key_node, deep=deep)
try:
hash(key)
except TypeError, exc:
raise yaml.constructor.ConstructorError('while constructing a mapping',
node.start_mark, 'found unacceptable key (%s)' % exc, key_node.start_mark)
value = self.construct_object(value_node, deep=deep)
mapping[key] = value
return mapping
更新：该库有利于yamlloader（这是基于yamlordereddictloader）已过时
我刚刚发现这是基于这个问题的答案创建，使用很简单一个Python库（https://pypi.python.org/pypi/yamlordereddictloader/0.1.1）：
import yaml
import yamlordereddictloader
datas = yaml.load(open('myfile.yml'), Loader=yamlordereddictloader.Loader)
在我的PyYaml安装的Python 2.7我更新__init__.py，constructor.py和loader.py。现在支持加载命令object_pairs_hook选项。我所做的更改的差异如下。
__init__.py
$ diff __init__.py Original
64c64
< def load(stream, Loader=Loader, **kwds):
---
> def load(stream, Loader=Loader):
69c69
< loader = Loader(stream, **kwds)
---
> loader = Loader(stream)
75c75
< def load_all(stream, Loader=Loader, **kwds):
---
> def load_all(stream, Loader=Loader):
80c80
< loader = Loader(stream, **kwds)
---
> loader = Loader(stream)
constructor.py
$ diff constructor.py Original
20,21c20
< def __init__(self, object_pairs_hook=dict):
< self.object_pairs_hook = object_pairs_hook
---
> def __init__(self):
27,29d25
< def create_object_hook(self):
< return self.object_pairs_hook()
<
54,55c50,51
< self.constructed_objects = self.create_object_hook()
< self.recursive_objects = self.create_object_hook()
---
> self.constructed_objects = {}
> self.recursive_objects = {}
129c125
< mapping = self.create_object_hook()
---
> mapping = {}
400c396
< data = self.create_object_hook()
---
> data = {}
595c591
< dictitems = self.create_object_hook()
---
> dictitems = {}
602c598
< dictitems = value.get('dictitems', self.create_object_hook())
---
> dictitems = value.get('dictitems', {})
loader.py
$ diff loader.py Original
13c13
< def __init__(self, stream, **constructKwds):
---
> def __init__(self, stream):
18c18
< BaseConstructor.__init__(self, **constructKwds)
---
> BaseConstructor.__init__(self)
23c23
< def __init__(self, stream, **constructKwds):
---
> def __init__(self, stream):
28c28
< SafeConstructor.__init__(self, **constructKwds)
---
> SafeConstructor.__init__(self)
33c33
< def __init__(self, stream, **constructKwds):
---
> def __init__(self, stream):
38c38
< Constructor.__init__(self, **constructKwds)
---
> Constructor.__init__(self)
有一个PyYAML ticket关于这个问题的5年前开业。它包含了一些相关的链接，包括链接到过这个问题:)我个人抓住gist 317164和修改了它一点点地从Python 2.7版使用OrderedDict，不包含的实现（只是替换from collections import OrderedDict类）。
这里有一个简单的解决方案，同时检查你的地图复制的顶级键。
import yaml
import re
from collections import OrderedDict
def yaml_load_od(fname):
"load a yaml file as an OrderedDict"
# detects any duped keys (fail on this) and preserves order of top level keys
with open(fname, 'r') as f:
lines = open(fname, "r").read().splitlines()
top_keys = []
duped_keys = []
for line in lines:
m = re.search(r'^([A-Za-z0-9_]+) *:', line)
if m:
if m.group(1) in top_keys:
duped_keys.append(m.group(1))
else:
top_keys.append(m.group(1))
if duped_keys:
raise Exception('ERROR: duplicate keys: {}'.format(duped_keys))
# 2nd pass to set up the OrderedDict
with open(fname, 'r') as f:
d_tmp = yaml.load(f)
return OrderedDict([(key, d_tmp[key]) for key in top_keys])