Python - inherit default class value if the variable has a specific value

A very simple problem, yet I need some assistance. I have created a class that has some default values. After that an instance takes the values based on an input. If one of the properties is "null" how can I assign the default value to it?

class Dragon:
    dragons=[]

    def __init__(self,dragon_type,name,health=2000,attack=450,fly_speed=120):
        self.dragon_type=dragon_type
        self.name=name
        self.health=health
        self.attack=attack
        self.fly_speed=fly_speed

        Dragon.dragons.append(self)

num=int(input())

for n in range(num):
    entry=input().split() #fire Azzaaxx null 480 null
    dragon_type,name,health,attack,fly_speed=entry[0],entry[1],entry[2],entry[3],entry[4]
    if health=="null":
        health=... #2000
    else:
        health=int(health)
    if attack=="null":
        attack=... #450
    else:
        attack=int(attack)
    if fly_speed=="null":
        fly_speed=... #120
    else:
        fly_speed=int(fly_speed)
    obj=Dragon(dragon_type,name,health,attack,fly_speed)

Is this approach acceptable or this should be defined differently?
Thank you in advance!

Change the class definition so that None values are converted to the default.

class Dragon:
    dragons=[]

    def __init__(self,dragon_type,name,health=None,attack=None,fly_speed=None):
        self.dragon_type=dragon_type
        self.name=name
        self.health=health if health is not None else 2000
        self.attack=attack if attack is not None else 450
        self.fly_speed=fly_speed if fly_speed is not None else 120

        Dragon.dragons.append(self)

Then you can set the variables in the caller to None if the user enters null, and the __init__() method will do the right thing, so you don't have to repeat the default values.

Build up a dictionary of non-null values to use as keyword arguments.

args = {}
if health != "null":
    args['health'] = int(health)
if attack != "null":
    args['attack'] = int(attack)
if fly_speed != "null":
    args['fly_speed'] = int(fly_speed)


obj = Dragon(dragon_type, name, **args)

However, this is a good opportunity to move the handling of "missing" values to a class method. __init__ should require values; the class method will provide defaults when its own input is lacking.

class Dragon:
    dragons = []

    def __init__(self, dragon_type, name, health: int, attack: int, fly_speed: int):
        self.dragon_type = dragon_type
        self.name = name
        self.health = health
        self.attack = attack
        self.fly_speed = fly_speed

        Dragon.dragons.append(self)

    @classmethod
    def from_input(cls):
        entry = input().split()

        health = int(entry[2]) if entry[2] != "null" else 2000
        attack = int(entry[3]) if entry[3] != "null" else 450
        speed = int(entry[4]) if entry[4] != "null" else 120

        return cls(entry[0], entry[1], health, attack, speed)


num = int(input())

for n in range(num):
    obj = Dragon.from_input()