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title: 零碎的小问题
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date: 2021-08-16 17:40:28
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updated: 2022-08-11 09:33:52
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---
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### python中的__future__包
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__future__是py2的概念,对应于py2,py3就是future,这是为了在是py2的时候还能用到一些新版本的特性而做成的包。意思禁用py2的import特性改成用py3的import的特性。
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- from future import absolute_import的作用:
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这是相对引用和绝对引用的概念,从相对导入变成绝对导入,大概意指你每次用import X时候都是在sys.path(即python的搜索模块的路径集)里面找X包。只要知道py3的import用法,加上这句话py2时候也能按照py3的import语法去正常使用。
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- from future import division的作用:
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division(精确除法),当我们没有在程序中导入该特征时,"/"操作符执行的是截断除法(Truncating Division), 当我们导入精确除法之后,"/"执行的是精确除法,如下所示:
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```python
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>>> 3/4
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0
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>>> from __future__ import division
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>>> 3/4
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0.75
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# 导入精确除法后,若要执行截断除法,可以使用"//"操作符:
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>>> 3//4
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0
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>>>
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```
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- from future import print_function的用法:
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超前使用python3的print函数。
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```python
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# 在python2.x的环境是使用下面语句
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from __future__ import print_function
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print('you are good') # 语法检查通过
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print 'you are good' # 语法检查失败
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```
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>未完待续
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