September 2014
Intermediate to advanced
332 pages
6h 48m
Japanese
Content preview from Python文法詳解
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32
第 3 章 式とデータ型
spam is None
と、同一性チェックを行う
is
または
is not
演算子を使用するようにします。これは、
==
より
も
is
のほうが高速に動作しますし、
==
演算子は比較対象のオブジェクトで独自に実装できてしま
うので、必ずしも正しく判定できるとは限らないためです。
None
のように、型のオブジェクトが一つだけしか存在しないオブジェクトは
と呼ばれます。また、型のオブジェクトが一つしか存在しないように保証するデザイ
ンパターンは、と呼ばれます。Python ではシングルトン・パターンが多
く使われており、
None
だけではなく、後述の
bool
型や
ellipsis
型のオブジェクトもシングルトン
です。
3.4
Ellipsis
オブジェクト
Ellipsis
オブジェクトは
ellipsis
型のシングルトンオブジェクトです。元々、多次元配列など
を扱うサードパーティ製ライブラリなどで利用することを想定して作られたオブジェクトで、特に
利用方法や利用目的は定められていません。
しかし、
Python3
からは
...
というリテラルで
Ellipsis
オブジェクト
を記述できるようになり
ましたので、なにかおもしろい使い方が生まれてくるかもしれません。
>>> ...
Ellipsis
例えば、サンプルコードなどで、不要な部分を省略するときには、
def spam():
...
と、実装部分を
pass
ではなく
Ellipsis
で指定すると省略している雰囲気が出ますし、値を明確 ...
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