电脑/python/官方内置模块/csv模块.html

<!DOCTYPE html>
<html>
<head>
<!-- 2016-07-30 六 23:05 -->
<meta  charset="utf-8">
<meta  name="viewport" content="width=device-width, initial-scale=1">
<title>csv模块</title>
<meta  name="generator" content="Org-mode">
<meta  name="author" content="万泽(德山书生)">
<meta  name="description" content="制作者邮箱：a358003542@gmail.com"
>
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</style>
</head>
<body>
<div id="content">
<header>
<h1 class="title">csv模块</h1>
</header><nav id="table-of-contents">
<h2>Table of Contents</h2>
<div id="text-table-of-contents">
<ul>
<li><a href="#orgheadline1">1. 简介</a></li>
<li><a href="#orgheadline2">2. 方言总的讨论</a></li>
<li><a href="#orgheadline3">3. 我写的sv方言</a></li>
<li><a href="#orgheadline4">4. 另外两个类接口</a></li>
<li><a href="#orgheadline5">5. 测试例子</a></li>
</ul>
</div>
</nav>


<div class="outline-2">
<h2 id="orgheadline1">简介</h2>
<div class="outline-text-2" id="text-1">
<p>
csv（Comma Separated Values），逗号分隔值文件格式。虽然名字是逗号分隔值，而且csv的<a href="http://tools.ietf.org/html/rfc4180.html">RFC 4180标准</a> 也要求csv文件用逗号作为分隔，但我感觉这实际上降低了csv的灵活性，我更愿意接受一种广义的csv标准作为小型数据（主要侧重表格数据）的存储和交互方案。
</p>


<p>
我给自己定义的一种csv方言如下所示：
</p>

<ol class="org-ol">
<li>换行符表示每一行，每一行一条记录。我想这可能是所有csv都统一的一条，所以csv文件最好叫做行记录文件？</li>
<li>如果数据是数值那么只有float类型，不需要加双引号。法文的csv小数是这种 <code>3,14159</code> ，这也太不规范了，应该废弃。小数统一为点标记， <code>3.14</code> 。然后float型都需要加上.标记，即使是 <code>3</code> 这样的形式，也应写为 <code>3.0</code> 这样的形式。</li>
<li>如果数据是字符串，那么必须用双引号标记。</li>
<li>为了控制csv文件的简单性，除了float，str之外的不再提供额外的数据类型支持了。</li>
<li>基于前面的描述，那么每一行的记录实际上不加额外的分隔符，就使用空白字符（空格），各个数据也能很好的表示出来了。</li>
<li>整个csv数据视作一个列表，然后每一行视作列表的子元素，每一个子元素也是一个列表，表头为第一行。即这样的形式：[[表头],[],[]&#x2026;]</li>
<li>True,False会写成"True" "False"，None 对应"" 即空字符串。</li>
</ol>
</div>
</div>


<div class="outline-2">
<h2 id="orgheadline2">方言总的讨论</h2>
<div class="outline-text-2" id="text-2">
<p>
python3的官方文档链接在<a href="https://docs.python.org/3.4/library/csv.html">这里</a> ，wiki的csv页面对于基本规则讨论比较好了，链接在<a href="http://zh.wikipedia.org/zh/%E9%80%97%E5%8F%B7%E5%88%86%E9%9A%94%E5%80%BC">这里</a> 。那里讨论的规则主要是狭义的csv规则，比如必须逗号作为分隔等等。下面将讨论各种csv方言，也就是作为广义的csv来讨论。最后讨论我上面提及的我喜欢的那种csv方言。
</p>

<p>
python csv模块默认的csv方言是 <code>excel</code> ，其定义如下所示：
</p>
<pre>
class excel(Dialect):
    """Describe the usual properties of Excel-generated CSV files."""
    delimiter = ','
    quotechar = '"'
    doublequote = True
    skipinitialspace = False
    lineterminator = '\r\n'
    quoting = QUOTE_MINIMAL
register_dialect("excel", excel)
</pre>
<p>
一般程式导出的csv文件都是对应这里的excel方言，比如分隔符(delimiter)是逗号；引号符号(quotechar)是双引号；doublequote用于处理双引号在字符中的情况，如果设置为True，那么下面的情况：
</p>
<pre>
1997,Ford,E350,"Super, ""luxurious"" truck"
</pre>
<p>
第四项将会被正确处理。一般设置为True吧。
</p>

<p>
skipinitialspace选项，默认是False，因为这里是逗号作为分隔符。在空格作为分隔符时还有点意义，此时额外的空格将会被忽略。
</p>

<p>
lineterminator选项，对于这个 <code>\r\n</code> 看不太懂，一般就是 <code>\n</code> 吧。
</p>

<p>
quoting选项，这个选项有几个设置值：
</p>

<ul class="org-ul">
<li>csv.QUOTE_MINIMAL 意思是只有在需要的情况下才加上双引号，比如逗号在字符串里面，双引号在字符串里面，换行符号在字符串里面等等。</li>
<li>csv.QUOTE_ALL 意思是都加上双引号，即使是数字。</li>
<li>csv.QUOTE_NONNUMERIC 数字不加，字符串都加上双引号。（只有在这种情况下csv模块才会正确将数字解析为float类型）</li>
<li>csv.QUOTE_NONE 都不加（此时需要设置好escapechar选项）</li>
</ul>
</div>
</div>


<div class="outline-2">
<h2 id="orgheadline3">我写的sv方言</h2>
<div class="outline-text-2" id="text-3">
<p>
具体代码如下所示：
</p>
<div class="highlight"><pre><span></span><span class="ch">#!/usr/bin/env python3</span>
<span class="c1"># -*- coding: utf-8 -*-</span>

<span class="kn">import</span> <span class="nn">csv</span>

<span class="k">class</span> <span class="nc">sv</span><span class="p">(</span><span class="n">csv</span><span class="o">.</span><span class="n">Dialect</span><span class="p">):</span>
    <span class="n">delimiter</span> <span class="o">=</span> <span class="s1">&#39; &#39;</span><span class="c1">#一个空格</span>
    <span class="n">quotechar</span> <span class="o">=</span> <span class="s1">&#39;&quot;&#39;</span>
    <span class="n">doublequote</span> <span class="o">=</span> <span class="bp">True</span>
    <span class="n">skipinitialspace</span> <span class="o">=</span> <span class="bp">True</span>
    <span class="n">lineterminator</span> <span class="o">=</span> <span class="s1">&#39;</span><span class="se">\n</span><span class="s1">&#39;</span>
    <span class="n">quoting</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">QUOTE_NONNUMERIC</span>


<span class="n">csv</span><span class="o">.</span><span class="n">register_dialect</span><span class="p">(</span><span class="s2">&quot;sv&quot;</span><span class="p">,</span> <span class="n">sv</span><span class="p">)</span>
</pre></div>
<p>
其继承自csv的Dialect类，然后通过csv模块的register_dialect函数进行注册。
</p>

<p>
类里面就是前面谈及的一些参数设置，具体就是我在上面谈论的最简化的csv格式：delimiter设置为一个空格，skipinitialspace设置为True，这是必要的。然后重要的quoting设置为 <code>csv.QUOTE_NONNUMERIC</code> ，让除数字外的都加上双引号。
</p>
</div>
</div>

<div class="outline-2">
<h2 id="orgheadline4">另外两个类接口</h2>
<div class="outline-text-2" id="text-4">
<p>
此外还写了两个类接口，提供了一些方便的查看或设置数据的接口。
</p>
<div class="highlight"><pre><span></span><span class="k">class</span> <span class="nc">Reader</span><span class="p">():</span>
    <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span><span class="n">f</span><span class="p">,</span><span class="n">dialect</span><span class="o">=</span><span class="s1">&#39;sv&#39;</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">lines</span> <span class="o">=</span> <span class="p">[]</span>
        <span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="n">csv</span><span class="o">.</span><span class="n">reader</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">dialect</span><span class="p">):</span>
            <span class="n">line</span> <span class="o">=</span> <span class="p">[</span><span class="bp">self</span><span class="o">.</span><span class="n">to_float</span><span class="p">(</span><span class="n">e</span><span class="p">)</span> <span class="k">for</span> <span class="n">e</span> <span class="ow">in</span> <span class="n">line</span><span class="p">]</span>
            <span class="bp">self</span><span class="o">.</span><span class="n">lines</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">line</span><span class="p">)</span>

    <span class="k">def</span> <span class="nf">getrow</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span><span class="n">num</span><span class="p">):</span>
        <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">lines</span><span class="p">[</span><span class="n">num</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span>

    <span class="k">def</span> <span class="nf">getcol</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span><span class="n">head</span><span class="p">):</span>
        <span class="n">index</span> <span class="o">=</span> <span class="bp">self</span><span class="o">.</span><span class="n">getrow</span><span class="p">(</span><span class="mi">1</span><span class="p">)</span><span class="o">.</span><span class="n">index</span><span class="p">(</span><span class="n">head</span><span class="p">)</span>
        <span class="n">lst</span> <span class="o">=</span> <span class="p">[]</span>
        <span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">lines</span><span class="p">:</span>
            <span class="n">lst</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">line</span><span class="p">[</span><span class="n">index</span><span class="p">])</span>
        <span class="k">return</span> <span class="n">lst</span>

    <span class="k">def</span> <span class="nf">getdata</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">return</span> <span class="bp">self</span><span class="o">.</span><span class="n">lines</span>

    <span class="nd">@staticmethod</span>
    <span class="k">def</span> <span class="nf">to_float</span><span class="p">(</span><span class="n">e</span><span class="p">):</span>
        <span class="k">try</span><span class="p">:</span>
            <span class="k">return</span> <span class="nb">float</span><span class="p">(</span><span class="n">e</span><span class="p">)</span>
        <span class="k">except</span> <span class="ne">ValueError</span><span class="p">:</span>
            <span class="k">return</span> <span class="n">e</span>

<span class="k">class</span> <span class="nc">Writer</span><span class="p">():</span>
    <span class="k">def</span> <span class="nf">__init__</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span><span class="n">f</span><span class="p">,</span><span class="n">dialect</span><span class="o">=</span><span class="s1">&#39;sv&#39;</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">lines</span> <span class="o">=</span> <span class="p">[]</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">writer</span> <span class="o">=</span> <span class="n">csv</span><span class="o">.</span><span class="n">writer</span><span class="p">(</span><span class="n">f</span><span class="p">,</span> <span class="n">dialect</span><span class="p">)</span>

    <span class="k">def</span> <span class="nf">addrow</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span><span class="n">row</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">lines</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">row</span><span class="p">)</span>

    <span class="k">def</span> <span class="nf">addcol</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span><span class="n">col</span><span class="p">):</span>
        <span class="k">for</span> <span class="n">index</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">lines</span><span class="p">)):</span>
            <span class="bp">self</span><span class="o">.</span><span class="n">lines</span><span class="p">[</span><span class="n">index</span><span class="p">]</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">col</span><span class="p">[</span><span class="n">index</span><span class="p">])</span>

    <span class="k">def</span> <span class="nf">setrow</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span><span class="n">num</span><span class="p">,</span><span class="n">row</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">lines</span><span class="p">[</span><span class="n">num</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span> <span class="o">=</span> <span class="n">row</span>
    <span class="k">def</span> <span class="nf">setcol</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span><span class="n">num</span><span class="p">,</span><span class="n">col</span><span class="p">):</span>
        <span class="k">for</span> <span class="n">index</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="bp">self</span><span class="o">.</span><span class="n">lines</span><span class="p">)):</span>
            <span class="bp">self</span><span class="o">.</span><span class="n">lines</span><span class="p">[</span><span class="n">index</span><span class="p">][</span><span class="n">num</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span> <span class="o">=</span> <span class="n">col</span><span class="p">[</span><span class="n">index</span><span class="p">]</span>

    <span class="k">def</span> <span class="nf">set</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span><span class="n">row</span><span class="p">,</span><span class="n">col</span><span class="p">,</span><span class="n">e</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">lines</span><span class="p">[</span><span class="n">row</span><span class="o">-</span><span class="mi">1</span><span class="p">][</span><span class="n">col</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span> <span class="o">=</span> <span class="n">e</span>

    <span class="k">def</span> <span class="nf">setdata</span><span class="p">(</span><span class="bp">self</span><span class="p">,</span><span class="n">data</span><span class="p">):</span>
        <span class="bp">self</span><span class="o">.</span><span class="n">lines</span> <span class="o">=</span> <span class="n">data</span>

    <span class="k">def</span> <span class="nf">write</span><span class="p">(</span><span class="bp">self</span><span class="p">):</span>
        <span class="k">for</span> <span class="n">line</span> <span class="ow">in</span> <span class="bp">self</span><span class="o">.</span><span class="n">lines</span><span class="p">:</span>
            <span class="bp">self</span><span class="o">.</span><span class="n">writer</span><span class="o">.</span><span class="n">writerow</span><span class="p">(</span><span class="n">line</span><span class="p">)</span>
</pre></div>
</div>
</div>

<div class="outline-2">
<h2 id="orgheadline5">测试例子</h2>
<div class="outline-text-2" id="text-5">
<p>
根据上面的谈论，我们进行了如下测试例子：
</p>
<div class="highlight"><pre><span></span><span class="kn">from</span> <span class="nn">wanze.csv</span> <span class="kn">import</span> <span class="n">Reader</span><span class="p">,</span><span class="n">Writer</span>

<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">&#39;test.csv&#39;</span><span class="p">,</span><span class="n">newline</span><span class="o">=</span><span class="s1">&#39;&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
    <span class="n">reader</span> <span class="o">=</span> <span class="n">Reader</span><span class="p">(</span><span class="n">f</span><span class="p">,</span><span class="s1">&#39;excel&#39;</span><span class="p">)</span>
    <span class="n">data</span> <span class="o">=</span> <span class="n">reader</span><span class="o">.</span><span class="n">getdata</span><span class="p">()</span>
    <span class="k">print</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>

<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">&#39;test2.csv&#39;</span><span class="p">,</span><span class="s1">&#39;w&#39;</span><span class="p">,</span><span class="n">newline</span><span class="o">=</span><span class="s1">&#39;&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
    <span class="n">writer</span> <span class="o">=</span> <span class="n">Writer</span><span class="p">(</span><span class="n">f</span><span class="p">,</span><span class="s1">&#39;sv&#39;</span><span class="p">)</span>
    <span class="n">writer</span><span class="o">.</span><span class="n">setdata</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
    <span class="n">writer</span><span class="o">.</span><span class="n">write</span><span class="p">()</span>

<span class="k">with</span> <span class="nb">open</span><span class="p">(</span><span class="s1">&#39;test2.csv&#39;</span><span class="p">,</span><span class="n">newline</span><span class="o">=</span><span class="s1">&#39;&#39;</span><span class="p">)</span> <span class="k">as</span> <span class="n">f</span><span class="p">:</span>
    <span class="n">reader</span> <span class="o">=</span> <span class="n">Reader</span><span class="p">(</span><span class="n">f</span><span class="p">)</span>
    <span class="n">data</span> <span class="o">=</span> <span class="n">reader</span><span class="o">.</span><span class="n">getdata</span><span class="p">()</span>
    <span class="k">print</span><span class="p">(</span><span class="n">data</span><span class="p">)</span>
</pre></div>

<p>
其中test.csv你随便找一个csv文件即可，这里假设它是最常见的excel csv格式，然后读入，然后将其写成前面提及的sv（Reader和Writer类的默认dialect），然后在读入。读者可以自己检验测试以下。
</p>

<p>
关于Reader和Writer类，提供了很多对应的函数接口，比如Reader类有
</p>
<ul class="org-ul">
<li>getrow 取某一行的值</li>
<li>getcol 取某一列的值</li>
<li>getdata 取整个表格的数据值，如下形式</li>
</ul>
<pre>
[['x', 'y'], [1.0, 2.0], [3.0, 4.0], [4.5, 5.5]]
</pre>

<p>
关于Writer类有：
</p>
<ul class="org-ul">
<li>addrow 添加一行值</li>
<li>addcol 添加一列值</li>
<li>set 设置某行某列的某个值为什么</li>
<li>setdata 设置整个表格为，即为如下形式[[][]&#x2026;]</li>
<li>write 实际写入到文件中去。</li>
</ul>
</div>
</div>
</div>
</body>
</html>