March 2018
Beginner to intermediate
624 pages
16h 10m
Japanese
Content preview from Head First Python 第2版 ―頭とからだで覚えるPythonの基本
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CountFromBy
の表現方法を定義する
__repr__
は特殊メソッドですが、組み込み関数
repr
としても利用できます。組み込み関
数
help
で
repr
の機能を調べると、「
Return the canonical string representation of the object.
」
（オブジェクトの印字可能な表現を含む文字列を返す）という説明でした。つまり、組み込み関
数
help
は
repr
（つまり
__repr__
）がオブジェクトの文字列バージョンを返す必要があると
言っているのです。
「オブジェクトの文字列バージョン」がどのようなものであるかは、オブジェクトがそれぞれ
何を行うかによります。クラスの
__repr__
メソッドを書くことでオブジェクトに何が起こ
るかを制御できます。
まずは、
CountFromBy
クラスに
__repr__
のための新たな
def
行を追加しましょう。
__repr__
は、必須の
self
以外の引数を取りません（
__repr__
はメソッドでしたね）。こ
の本のやり方に従い、このメソッドが文字列を返すことがわかるようにアノテーションも追加
しましょう。
クラスにこの短い関数を追加すると、インタプリタは
>>>
プロンプトで
CountFromBy
オブジェクトを表示するときは常にこの関数を使います。組み込み関数
print
も
__repr__
を使ってオブジェクトを表示します。
変更したコードを試す前に、前回の「試運転」で明らかになった別の問題を取り上げてみま
しょう。
def __repr__(self) ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
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.