[英]What is the difference between ! and !! in yaml?
I'm trying to load a YAML that looks like this: 我正在尝试加载看起来像这样的YAML:
dist: !!opencv-matrix
rows: 380
cols: 380
dt: f
data: [ 0., 0., -1.88644529e+18, 2.45423365e+00, 11698176.,
2.03862047e+00, -8.85501460e+10, 2.54738545e+00, 1.71208843e+20,
...
2.44447327e+00 ]
The loading code is just: 加载代码只是:
import yaml
y = yaml.load(s)
where s is the YAML loaded into a string. 其中s是加载到字符串中的YAML。
I get this error: 我收到此错误:
yaml.constructor.ConstructorError: could not determine a constructor for the tag 'tag:yaml.org,2002:opencv-matrix'
in "<string>", line 382, column 7:
dist: !!opencv-matrix
This is fair enough, so I add the constructor for that tag: 这很公平,所以我添加了该标记的构造函数:
def opencv_matrix(loader, node):
mapping = loader.construct_mapping(node)
mat = np.array(mapping["data"])
mat.resize(mapping["rows"], mapping["cols"])
return mat
yaml.add_constructor(u"!!opencv-matrix", opencv_matrix)
y = yaml.load(s)
I still get the error. 我仍然得到错误。 However, if I replace !!opencv_matrix with !opencv_matrix, then everything works. 但是,如果我用!opencv_matrix替换!! opencv_matrix,那么一切正常。
What's going on here? 这里发生了什么?
Secondary tags like !!opencv-matrix
are actually shorthand for tag:yaml.org,2002:opencv-matrix
(mentioned in the reference card ). 像!!opencv-matrix
这样的辅助标签实际上是tag:yaml.org,2002:opencv-matrix
简写tag:yaml.org,2002:opencv-matrix
(在参考卡中提到)。 It looks like PyYAML's add_constructor
method doesn't correctly handle this shorthand notation. 看起来PyYAML的add_constructor
方法无法正确处理这种速记符号。
This may be a bug, depending on how secondary tags are interpreted (see second part below). 这可能是一个错误,具体取决于二级标记的解释方式(参见下面的第二部分)。 I've submitted a bug report here , and hopefully it will be addressed. 我在这里提交了一份错误报告,希望能够得到解决。
Primary tags like !opencv-matrix
are defined explicitly, and loading seem to work without any problems in PyYAML. 像!opencv-matrix
这样的主要标签是明确定义的,并且加载似乎在PyYAML中没有任何问题。
It works for me if you replace !!opencv-matrix
with tag:yaml.org,2002:opencv-matrix
in the add_constructor
call. 如果你使用tag:yaml.org,2002:opencv-matrix
在add_constructor
调用中替换!!opencv-matrix
,它对我add_constructor
。
As for the original question, AFAIK primary tags ( !
) are for user-defined types, while secondary tags ( !!
) are meant to represent standard language-independent types defined here (hence the long and fancy format). 至于原始问题,AFAIK主标签( !
)用于用户定义类型,而辅助标签( !!
)用于表示此处定义的标准语言无关类型(因此是长格式和花式格式)。
If this is an OpenCV-generated file, then maybe it would probably be simpler if these tags were changed to primary tags in the application. 如果这是一个OpenCV生成的文件,那么如果将这些标记更改为应用程序中的主标记可能会更简单。
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