Data type multiple children; randomized allocation

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http://ubuntuforums.org – I'm programming in Python, firstly. So, I have a class that I made. Each class has a number value. It has both multiple parents and multiple children, and add and subtract methods. When you add/take away from the children, it'll add/take away from the parents, too. That's not a big problem. However, when you take away from the object, I need some algorithms to determine which children to take from, and how much to take away from each. The number values are fractions.Fraction objects, for arbitrary precision. I'd like one that selects a random assortment that's at least semi-efficient (Hardware)