我需要为标记创建一个自定义构造函数。标签应接受列表以及列表的锚点。
示例,我想如何使用我的标签:
original: &value [1, 2, 3]
processed: !mytag *value
所以我为!mytag
创建了一个基本的构造函数,该构造函数返回输入序列:
import yaml
def my_constructor(loader, node):
return loader.construct_sequence(node)
yaml.Loader.add_constructor('!mytag', my_constructor)
但是当我尝试加载上面的YAML源时,出现错误:
>>> source = '''original: &value [1, 2, 3]
processed: !mytag *value'''
>>> yaml.load(source, yaml.Loader)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "<stdin>", line 3, in t
File "/usr/local/lib/python3.7/site-packages/yaml/__init__.py", line 114, in load
return loader.get_single_data()
File "/usr/local/lib/python3.7/site-packages/yaml/constructor.py", line 41, in get_single_data
node = self.get_single_node()
File "/usr/local/lib/python3.7/site-packages/yaml/composer.py", line 36, in get_single_node
document = self.compose_document()
File "/usr/local/lib/python3.7/site-packages/yaml/composer.py", line 55, in compose_document
node = self.compose_node(None, None)
File "/usr/local/lib/python3.7/site-packages/yaml/composer.py", line 84, in compose_node
node = self.compose_mapping_node(anchor)
File "/usr/local/lib/python3.7/site-packages/yaml/composer.py", line 127, in compose_mapping_node
while not self.check_event(MappingEndEvent):
File "/usr/local/lib/python3.7/site-packages/yaml/parser.py", line 98, in check_event
self.current_event = self.state()
File "/usr/local/lib/python3.7/site-packages/yaml/parser.py", line 439, in parse_block_mapping_key
"expected <block end>, but found %r" % token.id, token.start_mark)
yaml.parser.ParserError: while parsing a block mapping
in "test.yml", line 1, column 1
expected <block end>, but found '<alias>'
in "test.yml", line 2, column 19
神奇的是,如果我用方括号将锚点引用包围,则可以使用:
>>> source = '''original: &value [1, 2, 3]
processed: !mytag [*value]'''
>>> yaml.load(source, yaml.Loader)
{'original': [1, 2, 3], 'processed': [[1, 2, 3]]}
但这不是我想要的,我需要将原始列表传递给构造函数,而不是双列表。
UPD:双重列表也不起作用。即使我返回它,它也会在结果中显示为原始列表,但是如果尝试从构造函数访问它,那么在那个阶段它只是一个空列表:
>>> source = '''original: &value [1, 2, 3]
... processed: !mytag [*value]'''
>>>
>>> def my_constructor(loader, node):
... print(loader.construct_sequence(node))
... return loader.construct_sequence(node)
...
>>> yaml.Loader.add_constructor('!mytag', my_constructor)
>>>
>>> yaml.load(source, yaml.Loader)
[[]] # <--- this is the printed value
{'original': [1, 2, 3], 'processed': [[1, 2, 3]]} # <--- this is the returned value
有人知道怎么做吗?
Python 3.7.6PyYAML 5.3
附加序列正是您想要的。
请注意,YAML标记描述了节点的type,并且不处理指令。别名是指现有节点,它们的类型已经为[[即使]],但它们没有显式标签(您的原始序列例如将在YAML核心架构下标记为!!seq
)。现在,如果您希望标签的语义是“采用现有节点,并以某种方式对其进行转换”,则它描述了一个函数调用。函数调用本身就是一个结构,仅将其输入作为参数。因此,要对其进行正确建模,需要将参数放置在结构中,而顺序是执行此操作的最简单方法。您也可以通过映射来完成它:
original: &value [1, 2, 3]
processed: !mytag {input: *value}
但是更冗长。
然后在您的构造函数中,从周围的结构中提取参数并对其进行处理。
Edit:
这是访问引用列表的概念证明。我不确定为什么您必须手动导航到外部节点,这可能是PyYAML错误。import yaml
source = '''original: &value [1, 2, 3]
processed: !mytag [*value]'''
def my_constructor(loader, node):
assert isinstance(node, yaml.SequenceNode)
param = loader.construct_sequence(node.value[0], deep=True)
print(param)
# do something with the param here
return param
yaml.Loader.add_constructor('!mytag', my_constructor)
print(yaml.load(source, yaml.Loader))
输出:
[1, 2, 3]
{'original': [1, 2, 3], 'processed': [1, 2, 3]}