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title: 零碎的小问题
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date: 2020-08-16 17:40:28
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updated: 2022-8-26 13:50:01
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categories: 错误本
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---
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> 所有问题按`想起来/遇到`的顺序排列
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### 1. 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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### 2. latex中画文本框
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这里有个示例:
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```tex
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\begin{center}
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\fbox
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{\parbox{0.92\columnwidth}{
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\subsection*{Key Points}\label{key point}
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\begin{center}
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\begin{itemize}[left]
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\item 1
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\item 2
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\item 3
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\item 4
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\item 5
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\end{itemize}
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\end{center}}}
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\end{center}
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```
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渲染结果:
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>未完待续
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