Beginning Python - From Novice to Professional

150 CHAPTER 7 ■ MORE ABSTRACTION
■Note In Chapter 9, you see how classes can call methods in their superclasses (more specifically, the
constructors of their superclasses). Those methods are called directly on the class; they haven’t bound their
self parameter to anything and are therefore called unbound methods.
Throwing Methods Around
In the previous section, I showed how you could use a bound method just like a function
without losing the self parameter. That means that you can use methods in many of the fancy
ways that I’ve used functions previously, with handy tools such as map, filter, and reduce (see
the section “Throwing Functions Around” in Chapter 6). In this section, I provide some examples
of these capabilities. They should all be fairly self-explanatory.
Let’s start by creating a class:
class FoodExpert:
def init(self):
self.goodFood = []
def addGoodFood(self, food):
self.goodFood.append(food)
def likes(self, x):
return x in self.goodFood
def prefers(self, x, y):
x_rating = self.goodFood.index(x)
y_rating = self.goodFood.index(y)
if x_rating > y_rating:
return y
else:
return x
This class has more code than earlier examples, but it is still pretty simple. It is meant to
represent some sort of food expert (as the name implies) who likes only some types of food, and
likes some more than others.
The init method simply initializes the objects by giving them an attribute called goodFood
containing an empty list. The addGoodFood method adds a type of food to the list, where the first
food type added is the expert’s favorite, the next one is the second choice, and so on. The likes
method simply checks whether the expert likes a certain type of food (whether it has been
added to goodFood), and finally the prefers method is given two food types (both of which must
be liked) and returns the preferred one (based on their position in goodFood).
Now, let’s play. In the following example, a FoodExpert is created and its taste buds
initialized: