October 2017
Intermediate to advanced
832 pages
13h 34m
Japanese
Content preview from Fluent Python ―Pythonicな思考とコーディング手法
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20章属性ディスクリプタ
ディスクリプタを学べば、より多くのツールを活用できるようになるだけでなく、Pythonの仕組みをより深く理解でき、その設計のエレガントさが感じられるようになります。
——Raymond HettingerPythonの中心的な開発者にして達人公式ドキュメントの「Descriptor HowTo Guide」より[20-01]
ディスクリプタは、同じアクセスロジックを複数の属性で再利用する方法です。たとえば、Django ORMやSQL AlchemyなどのORMにおけるフィールド型はディスクリプタで、データベースレコードのフィールドとPythonオブジェクトの属性の間のデータの流れを管理します†1。
[†1] 監訳注：ORM（Object-Relational Mapping）については13.2節を参照。
ディスクリプタは、__get__、__set__、__delete__メソッドからなるプロトコルを実装するクラスです。propertyクラスは、これらのディスクリプタプロトコルをすべて実装しています。プロトコルではよくあることですが、部分的に実装してもかまいません。実際、現実に書かれたコードで目にするディスクリプタはほとんど__get__と__set__だけを実装しており、また多くは1つだけを実装しています。
ディスクリプタはPythonの際立った特徴であり、アプリケーションレベルだけでなく、言語のインフラストラクチャでも導入されています。プロパティ以外でディスクリプタを活用するPythonの機能にはメソッド、そしてclassmethodデコレータとstaticmethodデコレータがあります。Pythonの奥義を極めるには、ディスクリプタを理解しなければなりません。本章ではこれを説明します。 ...
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I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
I’ve been on the O’Reilly platform for more than eight years. I use a couple of learning platforms, but I'm on O'Reilly more than anybody else. When you're there, you start learning. I'm never disappointed.Amir M.
I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.