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Python-字典.html
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<div class="page-header"><h1>Python-字典</h1></div>
<div class="well small">Permalink: <a class="more" href="/Python-字典.html">1000-01-09 18:44:00+00:09</a>
by <a class="url fn" href="/author/shang-wei.html">商伟 </a>
in <a href="/category/python.html">Python</a>
tags: <a href="/tag/python.html">Python</a> </div>
<div><p>[TOC]</p>
<h4>字典的介绍</h4>
<div class="highlight"><pre><span></span><span class="n">info</span> <span class="o">=</span> <span class="p">{</span><span class="s1">'name'</span><span class="p">:</span><span class="s1">'班长'</span><span class="p">,</span> <span class="s1">'id'</span><span class="p">:</span><span class="mi">100</span><span class="p">,</span> <span class="s1">'sex'</span><span class="p">:</span><span class="s1">'f'</span><span class="p">,</span> <span class="s1">'address'</span><span class="p">:</span><span class="s1">'地球亚洲中国北京'</span><span class="p">}</span>
</pre></div>
<ul>
<li>字典和列表一样，也能够存储多个数据</li>
<li>列表中找某个元素时，是根据下标进行的</li>
<li>字典中找某个元素时，是根据'名字'（就是冒号:前面的那个值，例如上面代码中的'name'、'id'、'sex'）</li>
<li>字典的每个元素由2部分组成，键:值。例如 'name':'班长' ,'name'为键，'班长'为值</li>
</ul>
<h5>字典的添加操作</h5>
<ul>
<li>info['id'] = ‘shangwei’</li>
<li>如果在使用 <strong>变量名['键'] = 数据</strong> 时，这个“键”在字典中，不存在，那么就会新增这个元素</li>
</ul>
<h5>字典的删除操作</h5>
<ul>
<li>del</li>
<li>del删除指定的元素</li>
<li>clear()</li>
<li>:clear清空整个字典</li>
</ul>
<h5>字典的修改操作</h5>
<ul>
<li>字典的修改操作就是 通过key来进行修改</li>
<li>info['id'] = 123</li>
</ul>
<h5>字典的查找操作</h5>
<ul>
<li>直接查找key</li>
<li>info['age']</li>
<li>如果字典存在key 返回他的 value 不存在则报错</li>
<li>在我们不确定字典中是否存在某个键而又想获取其值时，可以使用get方法，还可以设置默认值</li>
<li>age = info.get('age') #'age'键不存在，所以age为None</li>
<li>age = info.get('age', 18) # 若info中不存在'age'这个键，就返回默认值18</li>
</ul>
<h5>字典的常见操作</h5>
<ul>
<li>keys</li>
<li>返回一个包含字典所有KEY的列表</li>
<li>values</li>
<li>返回一个包含字典所有VALUE的列表</li>
<li>items</li>
<li>返回一个包含所有（键，值）元祖的列表</li>
<li>has_key （Python3 已取消）</li>
<li>dict.has_key(key)如果key在字典中，返回True，否则返回False</li>
</ul>
<h5>遍历</h5>
<ul>
<li>我们可以用 for 循环来遍历字典</li>
</ul>
<h5>enumerate()</h5>
<blockquote>
<p>enumerate() 函数用于将一个可遍历的数据对象(如列表、元组或字符串)组合为一个索引序列，同时列出数据和数据下标，一般用在 for 循环当中。</p>
</blockquote>
<div class="highlight"><pre><span></span><span class="n">chars</span> <span class="o">=</span> <span class="p">[</span><span class="s1">'a'</span><span class="p">,</span> <span class="s1">'b'</span><span class="p">,</span> <span class="s1">'c'</span><span class="p">,</span> <span class="s1">'d'</span><span class="p">]</span>
<span class="k">for</span> <span class="n">i</span><span class="p">,</span> <span class="nb">chr</span> <span class="ow">in</span> <span class="nb">enumerate</span><span class="p">(</span><span class="n">chars</span><span class="p">):</span>
<span class="k">print</span> <span class="n">i</span><span class="p">,</span> <span class="nb">chr</span>
<span class="o">...</span>
<span class="mi">0</span> <span class="n">a</span>
<span class="mi">1</span> <span class="n">b</span>
<span class="mi">2</span> <span class="n">c</span>
<span class="mi">3</span> <span class="n">d</span>
</pre></div></div>
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