August 2017
Intermediate to advanced
500 pages
12h 3m
Japanese
Content preview from PythonとJavaScriptではじめるデータビジュアライゼーション
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44
2 章 Python と JavaScript 間の言語学習の橋渡し
...
def add():
nonlocal count
count += inc
...
Python 2
では、簡単なディクショナリのテクニックを使って閉じた変数を変更します。
def get_counter(inc):
vars = {'count': 0}
def add():
vars['count'] += inc
print('Current count: ' + str(vars['count']))
return add
vars
に新しい値を割り当てておらず、その代わりに既存のコンテナを変更しています。これは
ローカルスコープ外でも完全に有効なので、上のコードは正しく機能します。
このように、
JavaScript
プログラマはほとんど労力をかけずにクロージャのスキルを
Python
に
移行できます。用途は似ていますが、多くの便利な機能が含まれる豊かな言語である
Python
の方
が同じ問題に適用できる選択肢がたくさんあります。おそらく、クロージャの最も一般的な用途は
Python
のデコレータでしょう。
基本的には、デコレータは関数自体を変更せずに関数の効用を拡張する関数ラッパーです。こ
れは比較的高度な概念ですが、
Code Ship
の
Web
サイト（
http://thecodeship.com/patterns/
guide-to-python-function-decorators/
）の説明がわかりやすいでしょう。
2.4.9 ...
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