5.2. from module import を使ってのインポート

5.2. `from module import` を使ってのインポート

Python にはモジュールをインポートする方法が 2 つあります. 両方とも有用であり, それらの使い分けを知らなくてはなりません. 1 つの方法は, Section 2.4, “全てはオブジェクト” で既に見た import module です. もう 1 つの方法でも同じ結果は得ますが, わずかですが重要な違いがあります.

以下が基本的な from module import 構文です.


from UserDict import UserDict

これはあなたが愛して止まない import module 構文に似ていますが, but with an important difference: the attributes and methods of the imported module types are imported directly into the local namespace, so they are available directly, without qualification by module name. You can import individual items or use from module import * to import everything.


	`from module import *` in Python is like `use module` in Perl; `import module` in Python is like `require module` in Perl.


	`from module import ` in Python is like `import module.` in Java; `import module` in Python is like `import module` in Java.

Example 5.2. `import module` vs. `from module import`

>>> import types
>>> types.FunctionType             
<type 'function'>
>>> FunctionType                   
Traceback (innermost last):
  File "<interactive input>", line 1, in ?
NameError: There is no variable named 'FunctionType'
>>> from types import FunctionType 
>>> FunctionType                   
<type 'function'>

	The `types` module contains no methods; it just has attributes for each Python object type. Note that the attribute, `FunctionType`, must be qualified by the module name, `types`.
	`FunctionType` by itself has not been defined in this namespace; it exists only in the context of `types`.
	This syntax imports the attribute `FunctionType` from the `types` module directly into the local namespace.
	Now `FunctionType` can be accessed directly, without reference to `types`.

When should you use from module import?

If you will be accessing attributes and methods often and don't want to type the module name over and over, use from module import.
If you want to selectively import some attributes and methods but not others, use from module import.
If the module contains attributes or functions with the same name as ones in your module, you must use import module to avoid name conflicts.

Other than that, it's just a matter of style, and you will see Python code written both ways.


	Use `from module import *` sparingly, because it makes it difficult to determine where a particular function or attribute came from, and that makes debugging and refactoring more difficult.

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