为什么在类上定义 __getitem__ 使其在 python 中可迭代?

2022-01-10 00:00:00 python overloading iterator

问题描述

为什么在类上定义 __getitem__ 会使其可迭代?

Why does defining __getitem__ on a class make it iterable?

例如，如果我写:

class b:
  def __getitem__(self, k):
    return k

cb = b()

for k in cb:
  print k

我得到了输出:

0
1
2
3
4
5
6
7
8
...

我真的希望看到for k in cb:"返回错误

I would really expect to see an error returned from "for k in cb:"

解决方案

如果你看看 PEP234 定义迭代器，它说:

If you take a look at PEP234 defining iterators, it says:

1. An object can be iterated over with "for" if it implements
   __iter__() or __getitem__().

2. An object can function as an iterator if it implements next().

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