How to write a reviewer for PyYAML?

Question

I want to have a custom function that serializes arbitrary python objects, for example, as the json.dump function has an optional arg argument called "default", which should be the function that jum-dumper will call if the object is not json serializable.

I just want to make the equivalent of this from a json package.

json.dump(tests_dump, file('somefile', 'w+'), default = lambda x: x.__dict__) 

It looks like I need to write yaml.add_representer from PyYAML docs, but it's really not clear how to do this.

Answer 1

Here is an example for add_representer. Not sure if this is exactly what you want. Nonetheless...

 import yaml #Arbitrary Class class MyClass: def __init__(self, someNumber, someString): self.var1 = someNumber self.var2 = someString #define the representer, responsible for serialization def MyClass_representer(dumper, data): serializedData = str(data.var1) + "|" + data.var2 return dumper.represent_scalar('!MyClass', serializedData ) #'register' it yaml.add_representer(MyClass, MyClass_representer) obj = MyClass(100,'test') print ( 'original Object\nvar1:{0}, var2:{1}\n'.format(obj.var1, obj.var2) ) #serialize yamlData = yaml.dump(obj) print('serialized as:\n{0}'.format(yamlData) ) #Now to deserialize you need a constructor def MyClass_constructor(loader,node): value = loader.construct_scalar(node) someNumber,sep,someString = value.partition("|") return MyClass(someNumber,someString) #'register' it yaml.add_constructor('!MyClass', MyClass_constructor) #deserialize obj2 = yaml.load(yamlData) print ( 'after deserialization\nvar1:{0}, var2:{1}\n'.format(obj2.var1, obj2.var2) ) 

Of course, there is code duplication, and the code is not optimized. You can make these two functions part of your class, as well as implement __repr__ to get a printed representation that you can use to populate serializedData in MyClass_representer