电脑/python/第三方模块/python-magic模块.html

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<title>python-magic模块</title>
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<h1 class="title">python-magic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="#orgheadline3">2. 图片有效性检验</a>
<ul>
<li><a href="#orgheadline2">2.1. 使用imghdr模块</a></li>
</ul>
</li>
</ul>
</div>
</nav>


<div class="outline-2">
<h2 id="orgheadline1">简介</h2>
<div class="outline-text-2" id="text-1">
<p>
python-magic模块的github地址在 <a href="https://github.com/ahupp/python-magic">这里</a> 。其可以看作linux下file命令的模拟（不过这个模块在windows和OS X系统下似乎也有支持）。有兴趣的可以先看看linux下file命令的使用效果。
</p>

<pre>
file test.pdf
</pre>

<pre>
&gt;&gt;&gt;file test.pdf
test.pdf: PDF document, version 1.2
</pre>

<p>
这个模块也没什么官方文档，不过好在使用还是很简单的。如下所示:
</p>
<pre>
&gt;&gt;&gt; import magic
&gt;&gt;&gt; magic.from_file("testdata/test.pdf")
'PDF document, version 1.2'
&gt;&gt;&gt; magic.from_buffer(open("testdata/test.pdf").read(1024))
'PDF document, version 1.2'
&gt;&gt;&gt; magic.from_file("testdata/test.pdf", mime=True)
'application/pdf'
</pre>
</div>
</div>


<div class="outline-2">
<h2 id="orgheadline3">图片有效性检验</h2>
<div class="outline-text-2" id="text-2">
<p>
之前用pillow处理一张图片后来出错了，很是纠结，然后发现原来这张图片格式有误，用本地的所有图片查看器包括浏览器都打不开。刚开始想法是用pillow试探性open来检验图片有效性。后来发现原来file命令是可以发现这些图片格式有误的。如下所示:
</p>

<pre>
&gt;&gt;&gt; magic.from_file("test_ok.jpg", mime=True)
'image/jpeg'
&gt;&gt;&gt; magic.from_file("test_bad.jpg", mime=True)
'application/octet-stream'
&gt;&gt;&gt; magic.from_file("test_png.jpg", mime=True)
'image/png'
&gt;&gt;&gt; magic.from_file("test_jpg.png", mime=True)
'image/jpeg'
</pre>

<p>
这里分为几种情况:
</p>
<ol class="org-ol">
<li>图片类型是jpg，后缀可能是jpg或者JPG或者jpeg之类的，在使用上没有什么麻烦，但可以考虑后缀名修复。</li>
<li>图片完全格式错误，也就是不是image/what，这种情况下这个图片是完全不能用的。</li>
<li>图片后缀是jpg，实际图片是png格式；或者图片后缀是png，实际图片是jpg格式。这在使用上可能某些浏览器能够正常打开，可能不行，可能某些图片查看器可以正常打开，也可能会出现问题。这些情况推荐统一和情况一一样进行图片后缀名修复。</li>
</ol>
</div>


<div class="outline-3">
<h3 id="orgheadline2">使用imghdr模块</h3>
<div class="outline-text-3" id="text-2-1">
<p>
当然就作为图片有效性检验这个问题，可能使用python-magic模块有点杀鸡用牛刀了。python官方内置模块imghdr已经能够很好地胜任这个工作了。
</p>

<pre>
&gt;&gt;&gt; import imghdr
&gt;&gt;&gt; imghdr.what("test_bad.jpg")
&gt;&gt;&gt; bool(imghdr.what("test_bad.jpg"))
False
&gt;&gt;&gt; imghdr.what("test_ok.jpg")
'jpeg'
&gt;&gt;&gt; imghdr.what("test_jpg.png")
'jpeg'
&gt;&gt;&gt; bool(imghdr.what("test_bad.jpg"))
False
&gt;&gt;&gt; imghdr.what("test_png.jpg")
'png'
</pre>

<p>
如果imghdr不能识别该图片类型:
</p>
<pre>
'rgb'	SGI ImgLib Files
'gif'	GIF 87a and 89a Files
'pbm'	Portable Bitmap Files
'pgm'	Portable Graymap Files
'ppm'	Portable Pixmap Files
'tiff'	TIFF Files
'rast'	Sun Raster Files
'xbm'	X Bitmap Files
'jpeg'	JPEG data in JFIF or Exif formats
'bmp'	BMP files
'png'	Portable Network Graphics
</pre>
<p>
其将返回False——可视为不认为其为有效图片。这大部分时候应该已经能够满足你的需要了，但如果你需要处理svg图片:
</p>

<pre>
&gt;&gt;&gt; imghdr.what("test02.svg")
&gt;&gt;&gt; import magic
&gt;&gt;&gt; magic.from_file("test02.svg", mime=True)
'image/svg+xml'
</pre>

<p>
那么imghdr是不支持的，而magic模块的分类更好一点。如果用imghdr模块能够解决你的问题，就用imghdr模块吧，如果不能满足你的要求那么再考虑使用magic模块。
</p>
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