Question

我有一个创建建筑的小班。我想了解更多关于 iter 的信息。以下作品：

class Building(object):
    def __init__(self, floors):
        self._floors = [None] * floors

    def __setitem__(self, floor_number, data):
        self._floors[floor_number] = data

    def __getitem__(self, floor_number):
        return self._floors[floor_number]

    def __iter__(self):
        for floor_number in self._floors:
            yield self._floors[floor_number]


building1 = Building(9)  # Construct a building with 9 floors
building1[0] = 'Reception'
building1[1] = 'ABC Corp'
building1[2] = 'DEF Inc'
building1[3] = 'Apple'
building1[4] = 'Cisco'
building1[5] = 'Microsoft'
building1[6] = 'Dell'
building1[7] = 'EMC'
building1[8] = 'HPE'

'''
for floor in building1:
    print(building1[floor])
'''

print(building1[6])

Dell

但如果我取消注释for循环，我会得到这个：

Traceback (most recent call last):
  File "C:/Users/Mark/PycharmProjects/main/main.py", line 28, in <module>
    for floor in building1:
  File "C:/Users/Mark/PycharmProjects/main/main.py", line 13, in __iter__
    yield self._floors[floor_number]
TypeError: list indices must be integers or slices, not str

我知道列表索引必须是整数。我没有得到的是为什么这个for循环违反了这个限制。

我想要做的是运用 iter 协议并打印出建筑物的每个楼层，而不仅仅是特定楼层。

Answer 1

你误解了for循环的作用;你没有索引，你在列表中有实际值。只是屈服于那些：

for contents in self._floors:
    yield contents

你需要在你的外循环中做同样的事情：

for contents in building1:
    print(contents)

Python for循环是Foreach loops，你迭代值而不是索引。

您的__iter__方法可以只返回列表的迭代器，而不是循环，有效地委托给iter()为您生成的列表迭代器：

def __iter__(self):
    return iter(self._floors)

使用iter协议的类

1 个答案: