__getitem__ 在 python 中重载 [英] __getitem__ overloading in python

问题描述

我试图理解 python 中的运算符重载，我编写了一个小程序，它重载 __getitem__() 方法并调用 for 循环:

类 Ovl:数据 = [1,2,3,4,5]def __getitem__(self, index):返回Hiii"x=Ovl()对于 x 中的项目:打印项目

这个程序进入无限循环打印Hiii".我想知道背后的原因.

解决方案

根据 object.__getitem__ 注意，

<块引用>

注意:for 循环期望对于非法索引IndexError 将引发 以允许正确检测到顺序.

<预><代码>>>>班级:... 数据 = [1,2,3,4,5]... def __getitem__(self, index):...如果指数 >= 5:...引发 IndexError('End')...返回Hiii"...>>>x=Ovl()>>>>>>对于 x 中的项目:...打印项目...嗨嗨嗨嗨嗨

I am trying to understand the operator overloading in python and I have written a small programs which overloads __getitem__() method and calls a for loop:

class Ovl:
    data = [1,2,3,4,5]
    def __getitem__(self, index):
        return "Hiii"

x=Ovl()

for item in x:
    print item

This program goes in to a infinite for loop printing "Hiii". I would like to know the reason behind it.

解决方案

According to the object.__getitem__ NOTE,

NOTE: for loops expect that an IndexError will be raised for illegal indexes to allow proper detection of the end of the sequence.

>>> class Ovl:
...     data = [1,2,3,4,5]
...     def __getitem__(self, index):
...         if index >= 5:
...             raise IndexError('End')
...         return "Hiii"
...
>>> x=Ovl()
>>>
>>> for item in x:
...     print item
...
Hiii
Hiii
Hiii
Hiii
Hiii

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