Question

I have a class with many attributes, and when I give a number, I would like it to subtract that from one attribute, but if the amount is greater than the attribute subtracted from, move to the next attribute with what is left over. Example:

def subt(self, amount):
    self.attr1 += amount
    if self.attr1 < 0:
        self.attr2 += self.attr1
        self.attr1 = 0
        if self.attr2 < 0:
            # etc...

It feel like there should be a concise recursive way to accomplish the same thing, but I don’t know how with the all the different attributes.

Answer 1

You can access the attributes using .__dict__ You need a list for the order you want to subtract. Something like this works.

class A():
    def __init__(self):
        self.foo = 100
        self.bar = 200
        self.baz = 300
        self.sub_stack = ['foo', 'baz', 'bar']

    def subt(self, amount):
        tmp_stack = self.sub_stack[:]
        while tmp_stack and amount:
            key = tmp_stack.pop(0)
            val = self.__dict__[key]
            if val > amount:
                self.__dict__[key] -= amount
                amount = 0
            else:
                amount -= self.__dict__[key]
                self.__dict__[key]=0
        return amount 

return value is the remainder on amount after iterating through your attributes