Question

Having a snippet like this:

import yaml
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.load(serialized_user)
print "name: %s, sname: %s" % (deserialized_user.name, deserialized_user.surname)

Yaml docs says that it is not safe to call yaml.load with any data received from an untrusted source; so, what should I modify to my snippet\class to use safe_load method?
Is it possible?

Answer 1

It appears that safe_load, by definition, does not let you deserialize your own classes. If you want it to be safe, I’d do something like this:

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

    def yaml(self):
       return yaml.dump(self.__dict__)

    @staticmethod
    def load(data):
       values = yaml.safe_load(data)
       return User(values["name"], values["surname"])

user = User('spam', 'eggs')
serialized_user = user.yaml()
print "serialized_user:  %s" % serialized_user.strip()

#Network
deserialized_user = User.load(serialized_user)
print "name: %s, sname: %s" % (deserialized_user.name, deserialized_user.surname)

The advantage here is that you have absolute control over how your class is (de)serialized. That means that you won’t get random executable code over the network and run it. The disadvantage is that you have absolute control over how your class is (de)serialized. That means you have to do a lot more work. 😉