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__future__ in Python

1. from __future__ import xxxx

这是为了在低版本的python中使用可能在某个高版本python中成为语言标准的特性，从而

在将代码由低版本迁移到高版本的过程中，减少需要做的工作。

这种语句被称为 future_statement 

2. future_statement的语法定义: Ref[2]

future_statement: "from" "__future__" "import" feature ["as" name]
                          ("," feature ["as" name])*

        feature: identifier
        name: identifier

3. 使用future_statement的注意事项

Reference

1. What is __future__ in Python used for and how/when to use it, and how it works

http://stackoverflow.com/questions/7075082/what-is-future-in-python-used-for-and-how-when-to-use-it-and-how-it-works

2. PEP 236 - PEP 236 -- Back to the __future__

https://www.python.org/dev/peps/pep-0236/

3. 28.11. __future__ — Future statement definitions

https://docs.python.org/2/library/__future__.html

4. Supporting Python 2 and 3 without 2to3 conversion

http://python3porting.com/noconv.html  (Porting to Python 3)

http://pypi.python.org/pypi/six

5. http://python-future.org/imports.html (To Read)

包括以下内容: 

• absolute_import: PEP 328: Imports: Multi-Line and Absolute/Relative
• division: PEP 238: Changing the Division Operator
• print_function: PEP 3105: Make print a function
• unicode_literals: PEP 3112: Bytes literals in Python 3000

XiaoKL学Python（C）__future__

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原文地址：http://www.cnblogs.com/cwgk/p/4446090.html