June 2026
Intermediate
804 pages
8h 21m
Japanese
Content preview from 入門 Python 3 第3版
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18章バイナリデータ
きちんとした質問には1桁の2進数で答えられる。0か1、すなわちイエスかノーだ。
—— カール・セーガン
テキストデータも扱いが難しいが、バイナリデータはまた違った面白さがある。ただし、エンディアン（コンピュータのCPUがデータをバイトに分割する際の方法）や整数の符号ビットなどの概念を知っておかなければならない。データを抽出したり変更したりするために、バイナリファイル形式やネットワークパケットの細部に踏み込む場合もある。本節ではバイナリデータ処理の基礎を説明する。バイナリファイルの読み書きの方法は「20章 ファイル」で取り上げる。
18.1 structによるバイナリデータの変換
今まで見てきたように、テキスト操作ツールは豊富に揃っている。それに比べて、バイナリデータのためのツールはずっと少ない。標準ライブラリにはCやC++の構造体に似たデータを処理するstructモジュールが含まれている。structを使えば、データ構造とバイナリデータを相互変換できる。
PNGファイルに含まれるデータを使って、この相互変換の仕組みを確認する。PNGはGIFやJPEGと並んで広く使われている画像形式である。ここではPNGデータから画像の幅と高さを抽出する小さなプログラムを作る。
素材としてはO'Reillyのロゴを使う。図18-1に示す小さなメガネザルである。
図18-1 O'Reillyのメガネザル
この画像のPNGファイルはWikipedia（https://bit.ly/orm-logo ...
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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.