如何拥有同时具有元组和字典特征的数据结构 [英] How to have data structure with both tuple and dictionary characteristic

问题描述

通过引用代码

http://initd.org/psycopg/docs/extras.html#dictionary-like-cursor

<预><代码>>>>rec['数据']abc'def">>>记录[2]abc'def"

我想知道他们是如何设法制作具有元组和字典特征的数据结构的?

解决方案

在 Python 中，[] 查找由 __getitem__ 魔术方法处理；换句话说，当您索引自定义类时，Python 将调用 instance.__getitem__(...) 并返回值.这可以让你做例如

<预><代码>>>>Foo类:... def __getitem__(self, value):... 返回值...>>>foo = foo()>>>foo[1"]'1'>>>富[0]0

有几种自然的方式来维护实际的数据结构；可能最简单的方法是维护一个字典和一个列表，并根据键的类型对其中之一进行索引.

注意这是不自然的；你会期望一个类似 dict 的对象将 0 视为一个键.可能值得编写一种不同的方法，例如index 处理索引.

您可能还希望实现 __setitem__ 和 __contains__ 方法.

By refering code at

http://initd.org/psycopg/docs/extras.html#dictionary-like-cursor

>>> rec['data']
"abc'def"
>>> rec[2]
"abc'def"

I was wondering how they manage to make a data structure having both tuple and dictionary characteristic?

解决方案

In Python the [] lookups are handled by the __getitem__ magic method; in other words, when you index a custom class Python will call instance.__getitem__(...) and return you the value. This lets you do e.g.

>>> class Foo:
...     def __getitem__(self, value):
...             return value
...
>>> foo = Foo()
>>> foo["1"]
'1'
>>> foo[0]
0

There are several natural ways of maintaining the actual data structure; probably the easiest is to maintain both a dict and a list and index into one of them depending on the type of the key.

Notice that this is unnatural; you would expect a dict-like object to treat 0 as a key. it might be worth writing a different method e.g. index to handle the indexing.

You may also wish to implement the __setitem__ and __contains__ methods.

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