version: 0.1 output: rst fix_inline_single_backquotes: true pdf: true # code_directory: ../_example — |

Dumping Python classes

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():

--- !python |

import sys import ruamel.yaml

class User(object):

def __init__(self, name, age):

self.name = name self.age = age

yaml = ruamel.yaml.YAML() yaml.register_class(User) yaml.dump([User(‘Anthon’, 18)], sys.stdout) — !stdout | which gives as output:: — | 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 to_yaml resp. from_yaml:

--- !python |

import sys import ruamel.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 = ruamel.yaml.YAML() yaml.register_class(User) yaml.dump([User(‘Anthon’, 18)], sys.stdout) — !stdout | which gives as output:

--- |

When using the decorator, which takes the YAML() instance as a parameter, the yaml = YAML() line needs to be moved up in the file:

--- !python |

import sys from ruamel.yaml 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().