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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fruits
pears
2
bananas
2
apple
10
「
in
」の代わりに「
not in
」を使う
前のページの最後で、ほとんどの
Python
プログラマは
in
の代わりに
not in
を使うよう
に元の
4
行のコードを書き直すと述べました。そこで
pears
キーの値をインクリメントす
る前に
pears
キーを
0
に設定し、その動作を確認してみましょう。
>>> if 'pears' not in fruits:
fruits['pears'] = 0
>>> fruits['pears'] += 1
>>> fruits
{'bananas': 2, 'pears': 1, 'apples': 10}
この
3
行で辞書が再び大きくなりました。現在、
fruits
辞書にはキーと値のペアが
3
つ
あります。
上の
3
行のコードは
Python
では一般的ですが、この
if/not in
の組み合わせをもっと便利で間違いを
起こしにくくする辞書メソッドを提供しています。
setdefault
メソッドはこの
2
行の
if/not in
文
と同じことを行いますが、コードは 1行で済みます。
以下は、このページの先頭の
pears
コードを
setdefault
を使って書き換えたものです。
>>> fruits.setdefault('pears', 0)
0
>>> fruits['pears'] += 1
>>> fruits
{'bananas': 2, 'pears': 2, 'apples': 10}
setdefault
の
1
回の呼び出しで
2
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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.