我无法在PyYAML文档中找到如何执行此操作。我想表示我在YAML中定义的python类,如果没有在YAML中指定,则在构造函数中为参数赋予默认值。例如:
>>> class Test(yaml.YAMLObject):
... yaml_tag = u"!Test"
... def __init__(self, foo, bar=3):
... self.foo = foo
... self.bar = bar
... def __repr__(self):
... return "%s(foo=%r, bar=%r)" % (self.__class__.__name__, self.foo, self.bar)
...
>>> yaml.load("""
... --- !Test
... foo: 5
... """)
Traceback (most recent call last):
File "<stdin>", line 4, in <module>
File "<stdin>", line 7, in __repr__
AttributeError: 'Test' object has no attribute 'bar'
我希望它会创建一个bar = 3的Test对象,但我猜它会在创建对象时绕过我的构造函数。如果我在YAML中包含bar的映射,那么一切都按预期工作:
>>> yaml.load("""
... --- !Test
... foo: 5
... bar: 42
... """)
Test(foo=5, bar=42)
有谁知道如何使用默认值?
答案 0 :(得分:9)
我遇到了同样的问题:yaml_tag由于某种原因无效。所以我使用了替代方法:
import yaml
def constructor(loader, node) :
fields = loader.construct_mapping(node)
return Test(**fields)
yaml.add_constructor('!Test', constructor)
class Test(object) :
def __init__(self, foo, bar=3) :
self.foo = foo
self.bar = bar
def __repr__(self):
return "%s(foo=%r, bar=%r)" % (self.__class__.__name__, self.foo, self.bar)
print yaml.load("""
- !Test { foo: 1 }
- !Test { foo: 10, bar: 20 }""")
输出:
[Test(foo=1, bar=3), Test(foo=10, bar=20)]
答案 1 :(得分:0)
基于alexanderlukanin13的回答。这是我的剪辑。
import yaml
YAMLObjectTypeRegistry = {}
def register_type(target):
if target.__name__ in YAMLObjectTypeRegistry:
print "{0} already in registry.".format(target.__name__)
elif 'yaml_tag' not in target.__dict__.keys():
print target.__dict__
raise TypeError("{0} must have yaml_tag attribute".format(
target.__name__))
elif target.__dict__['yaml_tag'] is None:
pass
else:
YAMLObjectTypeRegistry[target.__name__] = target
yaml.add_constructor(
target.__dict__['yaml_tag'],
lambda loader, node: target(**loader.construct_mapping(node)))
print "{0} added to registry.".format(target.__name__)
class RegisteredYAMLObjectType(type):
def __new__(meta, name, bases, class_dict):
cls = type.__new__(meta, name, bases, class_dict)
register_type(cls)
return cls
class RegisteredYAMLObject(object):
__metaclass__=RegisteredYAMLObjectType
yaml_tag = None
然后您可以像这样使用它:
class MyType(registry.RegisteredYAMLObject):
yaml_tag = u'!mytype'
def __init__(self, name, attr1='default1', attr2='default2'):
super(MyType, self).__init__()
self.name = name
self.attr1 = attr1
self.attr2 = attr2