Augmenting Methods: The Bad Way

Now, there are two ways we might code this Manager customization: a good way and a bad way. Let’s start with the bad way, since it might be a bit easier to understand. The bad way is to cut and paste the code of giveRaise in Person and modify it for Manager, like this:

class Manager(Person):
    def giveRaise(self, percent, bonus=.10):
        self.pay = int(self.pay * (1 + percent + bonus))   # Bad: cut-and-paste

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This works as advertised—when we later call the giveRaise method of a Manager instance, it will run this custom version, which tacks on the extra bonus. So what’s wrong with something that runs correctly?

The problem here is a very general one: any time you copy code with cut and paste, you essentially double your maintenance effort in the future. Think about it: because we copied the original version, if we ever have to change the way raises are given (and we probably will), we’ll have to change the code in two places, not one. Although this is a small and artificial example, it’s also representative of a universal issue—any time you’re tempted to program by copying code this way, you probably want to look for a better approach.