Question

I have a class defined like so:

class GameState:

    def __init__(self, state=None):
        if state is None:
            self.fps = 60
            self.speed = 1
            self.bounciness = 0.9
            self.current_level = None

            self.next_frame_time = 0
            self.init_time = 0
            self.real_time = 0
            self.game_time = 0

            self.game_events = []
            self.real_events = []
        else:
            # THIS being the key line:
            self.__dict__.update(**state)

Is there an interface I can define, such that this works (i.e. the ** operator works on my class):

>>> a = GameState()
>>> b = GameState(a)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: update() argument after ** must be a mapping, not GameState

Essentially, I want b to take on all of the attributes of a.

I didn’t think it would work, but I tried defining __getitem__ without any luck.

EDIT: I want to avoid using b’s __dict__, as I want to also be able to pass a dictionary as an argument, and potentially use ** on GameState objects elsewhere.

Answer 1

in order for **obj to work, you have to implement (or inherit) the __getitem__() and keys() methods.

def __getitem__(self, item):
    return self.__dict__[item] # you maybe should return a copy
def keys(self):
    return self.__dict__.keys() # you could filter those