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Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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14章イテラブル、イテレータ、ジェネレータ
同じものの繰り返しが自分のプログラムにあったら、私はそれを問題の兆候とみなします。プログラムの格好は、解決すべき問題だけを反映すべきです。コードに現れる規則性は、少なくとも私にとっては、私が十分に効果的に抽象化していないことの現れであり、しばしばそれは、マクロを書くべきところを手作業で展開してしまっていることを示しています。
——Paul GrahamLispハッカーにしてベンチャーキャピタリスト『Hackers & Painters』，13章「Revenge of the Nerds」より[EN-32][JP-14]
反復（繰り返し）はデータ処理の基本です。加えて、メモリに収まりきらないデータセットをスキャンするのなら、要素を怠惰に、つまり1回に1つずつその場その場で取ってくる方法が必要です。これがIteratorパターンです。本章では、Iteratorパターンがどのような形でPythonに組み込まれているかを説明することで、これを自力で実装する必要などないことを示します。
PythonにはLisp（Paul Grahamのお気に入りの言語）のようなマクロがないので、Iteratorパターンを抽象化するには、yieldキーワードの追加という言語仕様の変更が必要でした。このキーワードは、2001年にPython 2.2に追加されました†1。yieldキーワードを使えばジェネレータを構築でき、このジェネレータはイテレータとして動作します。
[†1] Python 2.2のユーザは、from __future__ import generatorsディレクティブでyieldを使用できます。yieldはPython 2.3からデフォルトで利用できます。 ...
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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.