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
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,
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.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.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.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.
in
で調べる
キー
No4
オブジェクト
キー
No1
オブジェクト
キー
No3
オブジェクト
キー
No2
オブジェクト
辞書
実行時の
KeyError
を避ける
リストの場合と同様、
in
演算子を使って辞書にキーがあるかどうかを調べることができま
す。インタプリタは、キーの有無によって
True
または
False
を返します。
これを利用して
KeyError
例外を回避してみましょう。実行時に辞書にデータを追加しよ
うとしている最中に、このエラーが生じた結果としてコードが止まると迷惑だからです。
このテクニックを実証するために、
fruits
という辞書を作成し、
in
演算子を使って存在し
ないキーにアクセスしたときに
KeyError
が起こらないようにします。まず、空の辞書を作成
します。そして、キー
apples
に値
10
を対応させて、辞書に追加します。
in
演算子を使って
キー
apples
の有無を確認できます。
>>> fruits = {}
>>> fruits['apples'] = 10
>>> fruits
{'apples': 10}
>>> 'apples' in fruits
True
上のコードを実行した後にインタプリタにはメモリ内の
fruits
辞書がどのように見える
かを考えてみましょう。
Q
：このページの例から、
Python
は
true
に定数
True
を使っているのですよね？
False
もあるのですか？
また、
これらの値を使うときに大文字小文字は重要なのですか？
A
：すべての質問に対してそのとおりです。
Python
でブール値
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,
and much more.
Read now
Unlock full access
More than 5,000 organizations count on O’Reilly
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.