我想让PyYAML的加载器将映射(和有序映射)加载到Python 2.7+ OrderedDict类型中,而不是dict
它当前使用的普通和对列表。
最好的方法是什么?
我想让PyYAML的加载器将映射(和有序映射)加载到Python 2.7+ OrderedDict类型中,而不是dict
它当前使用的普通和对列表。
最好的方法是什么?
Answers:
更新:在python 3.6+中OrderedDict
,由于新的dict实现已经在pypy中使用了一段时间(尽管现在考虑了CPython实现的细节),您可能根本不需要。
更新:在python 3.7+中,dict对象的插入顺序保留性质已声明为Python语言规范的正式组成部分,请参阅Python 3.7的新增功能。
我喜欢@James的简单解决方案。但是,它更改了默认的全局yaml.Loader
类,这可能导致麻烦的副作用。特别是在编写库代码时,这是一个坏主意。另外,它不能直接与使用yaml.safe_load()
。
幸运的是,无需付出太多努力即可改进该解决方案:
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,我不知道明显的概括,但是至少这应该没有任何副作用:
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模块允许您指定自定义“表示器”以将Python对象转换为文本,并指定“构造器”以逆转该过程。
_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)
from six import iteritems
,然后将其更改为iteritems(data)
使其在Python 2和3中同样有效
represent_dict
和DEFAULT_MAPPING_TAG
)的未记录功能。是因为文档不完整,还是不支持这些功能并且可能随时更改恕不另行通知?
dict_constructor
您需要致电loader.flatten_mapping(node)
否则您将无法加载<<: *...
(合并语法)
ruamel.yaml是PyYAML的替代品(免责声明:我是该软件包的作者)。保留映射的顺序是2015年在第一版(0.1)中添加的内容之一。它不仅保留字典的顺序,还保留注释,锚点名称,标签并支持YAML 1.2规范(2009年发布)
规范说,不能保证排序,但是YAML文件中当然有排序,并且适当的解析器可以仅保留该排序器,并透明地生成一个保持排序的对象。您只需要选择正确的解析器,加载器和转储器¹:
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
是CommentedMap
类似dict 的类型,但具有额外的信息,这些信息会一直保留直到被转储(包括保留的注释!)
CommentedMap
直接使用它,但是它不起作用,并且OrderedDict
将!!omap
其放置在每个地方都不是很友好。
CommentedMap
with 保存为safe=True
in YAML
,但该方法不起作用(使用safe=False
作品)。我也遇到CommentedMap
无法修改的问题,但现在无法重现...如果再次遇到此问题,我将打开一个新问题。
yaml = YAML()
,您将获得往返解析器/自卸车,这是派生安全分析器/自卸车,它知道CommentedMap /序列等
注意:有一个基于以下答案的库,该库还实现了CLoader和CDumpers:Phynix / yamlloader
我非常怀疑这是最好的方法,但这是我想出的方法,并且确实有效。也可作为要点。
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
key_node.start_mark
在错误消息中包含该属性,我看不出任何明显的方法可以简化您的中央构造循环。如果尝试利用OrderedDict
构造函数将接受键,值对的可迭代项的事实,则在生成错误消息时,您将无法访问该详细信息。
更新:不赞成使用该库,而推荐使用yamlloader(它基于yamlordereddictloader)
我刚刚找到了一个Python库(https://pypi.python.org/pypi/yamlordereddictloader/0.1.1),该库是基于此问题的答案而创建的,使用起来非常简单:
import yaml
import yamlordereddictloader
datas = yaml.load(open('myfile.yml'), Loader=yamlordereddictloader.Loader)
yodl
github。
在针对Python 2.7的For PyYaml安装中,我更新了__init __。py,constructor.py和loader.py。现在支持用于加载命令的object_pairs_hook选项。我所做的更改差异如下。
__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)
这是一个简单的解决方案,还可以检查地图中是否有重复的顶级键。
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])