电脑/python/官方内置模块/collections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>collections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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<header>
<h1 class="title">collections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. Counter对象</a></li>
<li><a href="#orgheadline2">2. namedtuple对象</a></li>
<li><a href="#orgheadline3">3. OrderedDict对象</a></li>
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<p>
collections模块里面有一些很有用的数据类型，更多信息请参看 <a href="https://docs.python.org/3.4/library/collections.html">官方文档</a> 。
</p>

<div class="outline-2">
<h2 id="orgheadline1">Counter对象</h2>
</div>


<div class="outline-2">
<h2 id="orgheadline2">namedtuple对象</h2>
<div class="outline-text-2" id="text-2">
<p>
namedtuple数据类型你可能已经在某处接触到了，其非常有用。比如说argparse模块里面parse命令行输入之后返回的就是一个namedtuple对象。
</p>

<p>
其使用和概念都很简单，没啥好说的。下面是一个例子（来自官方文档）:
</p>
<pre>
&gt;&gt;&gt; Point = namedtuple('Point', ['x', 'y'])
&gt;&gt;&gt; p = Point(11, y=22)     # instantiate with positional or keyword arguments
&gt;&gt;&gt; p[0] + p[1]             # indexable like the plain tuple (11, 22)
33
&gt;&gt;&gt; x, y = p                # unpack like a regular tuple
&gt;&gt;&gt; x, y
(11, 22)
&gt;&gt;&gt; p.x + p.y               # fields also accessible by name
33
&gt;&gt;&gt; p                       # readable __repr__ with a name=value style
Point(x=11, y=22)
</pre>
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</div>


<div class="outline-2">
<h2 id="orgheadline3">OrderedDict对象</h2>
<div class="outline-text-2" id="text-3">
<p>
python中的字典对象默认各个key是没有顺序的，OrderdDict对象的概念就是在字典概念的基础上让各个key有顺序。
</p>

<p>
一个例子如下所示（来自官方文档）。简单的理解就是一个字典对象记住了各个key的插入顺序。
</p>
<pre>
&gt;&gt;&gt; d = {'banana': 3, 'apple':4, 'pear': 1, 'orange': 2}

&gt;&gt;&gt; # dictionary sorted by key
&gt;&gt;&gt; OrderedDict(sorted(d.items(), key=lambda t: t[0]))
OrderedDict([('apple', 4), ('banana', 3), ('orange', 2), ('pear', 1)])

&gt;&gt;&gt; # dictionary sorted by value
&gt;&gt;&gt; OrderedDict(sorted(d.items(), key=lambda t: t[1]))
OrderedDict([('pear', 1), ('orange', 2), ('banana', 3), ('apple', 4)])

&gt;&gt;&gt; # dictionary sorted by length of the key string
&gt;&gt;&gt; OrderedDict(sorted(d.items(), key=lambda t: len(t[0])))
OrderedDict([('pear', 1), ('apple', 4), ('orange', 2), ('banana', 3)])
</pre>
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