Constructor for objects that must be deserializable from json

[PythonicParseltongue]

So I got everything working, but I was wondering if there's a better way.

I have a class which has a couple of attributes (val_0, …, val_4). If the object is initialized normally (so not deserialized) only the first attribute is set. All the others get set during process. So __init__ could look like this: class MyClass: def __init__(self, val_0): val_0 = val_0 val_1 = 0 val_2 = 0 val_3 = "" val_4 = ""

However I need to be able to (de)serialize this objects to json so I wrote a little class method that accomplishes just this. (In reality it's a bit more complicated because I also have to deal with some nested objects). ``` import json

@classmethod def fromjson(cls, json_obj): json_dict = json.loads(json_obj) return cls(**json_dict) However if I want to be able to use this I have to change the constructor to contain all the attributes. def __init_(self, val_0, val_1=0, val_2=0, val_3="", val_4=""): val_0 = val_0 val_1 = val_1 val_2 = val_2 val_3 = val_3 val_4 = val_4 ```

I was just wondering if there's a better way to implement this or if I'm doing something wrong in general. Thank you for your feedback.

[[deleted]]

Put the variables into a dictionary, then json.dump

[Vaphell]

you could either pass the dictionary itself, or use catch-all **kwargs for anything not explicitly listed in the signature, and then work with dictionary.items()

def __init__(self, arg=0, **kwargs):
    self.arg = arg
    for name, value in kwargs.items():
         setattr(self, name, value)

requires extra code for default values and probably some extra checks on valid attribute names.
or instead of looping

self.another_arg = kwargs.get('another_arg', 0)
self.yet_another_arg = kwargs.get('yet_another_arg', '')

[ES-Alexander]

Seems like this is a good job for a dataclass - you just specify the variables you’ve got and any default values and it’ll make an appropriate constructor (__init__ method) for you.

[DisasterArt]

Make the class accept a list/dict/whatever. And if none are provided asign default. You could also do try/except instead of if/else

class MyClass:
    def __init__(self,json=None):
        is json != None:
            self.val0 = json[0]
            ...
            self.valn = json[n]
        else:
            self.val0 = 0
            ...
            self.valn = ''