Dumping Python classesΒΆ
Only yaml = YAML(typ='unsafe')
loads and dumps Python objects out-of-the-box. And
since it loads any Python object, this can be unsafe.
If you have instances of some class(es) that you want to dump or load, it is
easy to allow the YAML instance to do that explicitly. You can either register the
class with the YAML
instance or decorate the class.
Registering is done with YAML.register_class()
:
import sys
import ruyaml
class User:
def __init__(self, name, age):
self.name = name
self.age = age
yaml = ruyaml.YAML()
yaml.register_class(User)
yaml.dump([User('Anthon', 18)], sys.stdout)
which gives as output:
- !User
name: Anthon
age: 18
The tag !User
originates from the name of the class.
You can specify a different tag by adding the attribute yaml_tag
, and
explicitly specify dump and/or load classmethods which have to be called
from_yaml
resp. from_yaml
:
import sys
import ruyaml
class User:
yaml_tag = u'!user'
def __init__(self, name, age):
self.name = name
self.age = age
@classmethod
def to_yaml(cls, representer, node):
return representer.represent_scalar(cls.yaml_tag,
u'{.name}-{.age}'.format(node, node))
@classmethod
def from_yaml(cls, constructor, node):
return cls(*node.value.split('-'))
yaml = ruyaml.YAML()
yaml.register_class(User)
yaml.dump([User('Anthon', 18)], sys.stdout)
which gives as output:
- !user Anthon-18
When using the decorator, which takes the YAML()
instance as a parameter,
the yaml = YAML()
line needs to be moved up in the file:
import sys
from ruyaml import YAML, yaml_object
yaml = YAML()
@yaml_object(yaml)
class User:
yaml_tag = u'!user'
def __init__(self, name, age):
self.name = name
self.age = age
@classmethod
def to_yaml(cls, representer, node):
return representer.represent_scalar(cls.yaml_tag,
u'{.name}-{.age}'.format(node, node))
@classmethod
def from_yaml(cls, constructor, node):
return cls(*node.value.split('-'))
yaml.dump([User('Anthon', 18)], sys.stdout)
The yaml_tag
, from_yaml
and to_yaml
work in the same way as when using
.register_class()
.