In python, how do I cast a class object to a dict

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Let"s say I"ve got a simple class in python

class Wharrgarbl(object):
    def __init__(self, a, b, c, sum, version="old"):
        self.a = a
        self.b = b
        self.c = c
        self.sum = 6
        self.version = version

    def __int__(self):
        return self.sum + 9000

    def __what_goes_here__(self):
        return {"a": self.a, "b": self.b, "c": self.c}

I can cast it to an integer very easily

>>> w = Wharrgarbl("one", "two", "three", 6)
>>> int(w)
9006

Which is great! But, now I want to cast it to a dict in a similar fashion

>>> w = Wharrgarbl("one", "two", "three", 6)
>>> dict(w)
{"a": "one", "c": "three", "b": "two"}

What do I need to define for this to work? I tried substituting both __dict__ and dict for __what_goes_here__, but dict(w) resulted in a TypeError: Wharrgarbl object is not iterable in both cases. I don"t think simply making the class iterable will solve the problem. I also attempted many googles with as many different wordings of "python cast object to dict" as I could think of but couldn"t find anything relevant :{

Also! Notice how calling w.__dict__ won"t do what I want because it"s going to contain w.version and w.sum. I want to customize the cast to dict in the same way that I can customize the cast to int by using def int(self).

I know that I could just do something like this

>>> w.__what_goes_here__()
{"a": "one", "c": "three", "b": "two"}

But I am assuming there is a pythonic way to make dict(w) work since it is the same type of thing as int(w) or str(w). If there isn"t a more pythonic way, that"s fine too, just figured I"d ask. Oh! I guess since it matters, this is for python 2.7, but super bonus points for a 2.4 old and busted solution as well.

There is another question Overloading __dict__() on python class that is similar to this one but may be different enough to warrant this not being a duplicate. I believe that OP is asking how to cast all the data in his class objects as dictionaries. I"m looking for a more customized approach in that I don"t want everything in __dict__ included in the dictionary returned by dict(). Something like public vs private variables may suffice to explain what I"m looking for. The objects will be storing some values used in calculations and such that I don"t need/want to show up in the resulting dictionaries.

UPDATE: I"ve chosen to go with the asdict route suggested but it was a tough choice selecting what I wanted to be the answer to the question. Both @RickTeachey and @jpmc26 provided the answer I"m going to roll with but the former had more info and options and landed on the same result as well and was upvoted more so I went with it. Upvotes all around though and thanks for the help. I"ve lurked long and hard on stackoverflow and I"m trying to get my toes in the water more.

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