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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12
章 高度なイテレーション
you are here
483
メソッド呼び出しをつなげるときには注意する
（前述の例の
strip
と
split
のように）
Python
のメソッド呼び出しをつなぐことを嫌う人も
います。このようなチェーンは、一見読みにくいからです。しかし、メソッドチェーンはよく使わ
れているので、遭遇することも多いでしょう。しかし、メソッド呼び出しの順序は交換できないの
で注意が必要です。
次のコードは問題が起こる例です（この例は前ページのコードによく似ています）。前は
strip
、
split
という順序でしたが、今回はまず
split
を呼び出してから
strip
を呼び出して
います。詳しく説明しましょう。
AttributeError
を
起こしてクラッシュ
します。
このメソッド
チェーンの順序が
前とは逆です。
ここでは何が起こっているのでしょうか？
まず、メソッドチェーンの実行時における代入演算
子の右辺のデータ型を考えてください。
実行前の
line
は文字列です。文字列に対して
split
を呼び出すと、
split
に指定した引数
を区切り文字として使って文字列のリストを返します。最初は文字列（
line
）だったものが動的
にリストに変わり、そのリストに対して別のメソッドを呼び出します。この例では、次のメソッ
ドは
strip
です。
strip
はリストではなく文字列に対して呼び出すものなので、リストにはメ
ソッド
strip
がないため
AttributeError
となります。
前ページのメソッドチェーンにはこの問題はありません。 ...
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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.