How to deserialize an object with PyYAML using safe_load?

Question

Having a snippet like this:

import yaml
class User(object):
    def __init__(self, name, surname):
       self.name= name
       self.surname= surname

user = U         


        

Answer 1

If you have many tags and don't want to create objects for all of them, or in case you don't care about the actual type returned, only about dotted access, you catch all undefined tags with the following code:

import yaml

class Blob(object):
    def update(self, kw):
        for k in kw:
            setattr(self, k, kw[k])

from yaml.constructor import SafeConstructor

def my_construct_undefined(self, node):
    data = Blob()
    yield data
    value = self.construct_mapping(node)
    data.update(value)

SafeConstructor.add_constructor(None, my_construct_undefined)


class User(object):
    def __init__(self, name, surname):
        self.name= name
        self.surname= surname

user = User('spam', 'eggs')
serialized_user = yaml.dump(user)
#Network
deserialized_user = yaml.safe_load(serialized_user)
print "name: %s, sname: %s" % (deserialized_user.name, deserialized_user.surname)

In case you wonder why the my_construct_undefined has a yield in the middle: that allows for instantiating the object separately from creation of its children. Once the object exist it can be referred to in case it has an anchor and of the children (or their children) a reference. The actual mechanisme to create the object first creates it, then does a next(x) on it to finalize it.