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python - python中的映射方法

转载 作者:太空狗 更新时间:2023-10-29 20:35:24 25 4
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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

声明这个类之后,我写了这段代码:

>>> f = FoodExpert()
>>> f.init()
>>> map(f.addGoodFood, ['SPAM', 'Eggs', 'Bacon', 'Rat', 'Spring Surprise'])
[None, None, None, None, None]

>>> f.goodFood
['SPAM', 'Eggs', 'Bacon', 'Rat', 'Spring Surprise']

我无法理解 map 函数在幕后是如何工作的,为什么它返回一个包含所有 None 的列表,但是当我检查 f.goodFood 时那里添加了元素?

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