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title="Permalink to [雪峰磁针石博客]python3快速入门教程2数据结构3列表">[雪峰磁针石博客]python3快速入门教程2数据结构3列表</a></h1>
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<abbr class="published" title="2018-09-02T10:35:00+08:00">
Published: 日 02 九月 2018
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By <a class="url fn" href="/author/andrew.html">andrew</a>
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<p>In <a href="/category/python.html">python</a>.</p>
</footer><!-- /.post-info --> <h2 id="_1">快速入门</h2>
<p>Python有一些复合数据类型，用于组合值。最常用的是 list(列表))，为中括号之间的逗号分隔的值。列表的元素可以是多种类型，但是通常是同一类型。</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">squares</span> <span class="o">=</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">9</span><span class="p">,</span> <span class="mi">16</span><span class="p">,</span> <span class="mi">25</span><span class="p">]</span>
<span class="o">>>></span> <span class="n">squares</span>
<span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">9</span><span class="p">,</span> <span class="mi">16</span><span class="p">,</span> <span class="mi">25</span><span class="p">]</span>
</pre></div>
<p>像字符串和其他序列类型，列表可支持切片和索引:</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">squares</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="c1"># indexing returns the item</span>
<span class="mi">1</span>
<span class="o">>>></span> <span class="n">squares</span><span class="p">[</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span>
<span class="mi">25</span>
<span class="o">>>></span> <span class="n">squares</span><span class="p">[</span><span class="o">-</span><span class="mi">3</span><span class="p">:]</span> <span class="c1"># slicing returns a new list</span>
<span class="p">[</span><span class="mi">9</span><span class="p">,</span> <span class="mi">16</span><span class="p">,</span> <span class="mi">25</span><span class="p">]</span>
</pre></div>
<p>切片返回新的列表，下面操作返回列表a的浅拷贝:</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">squares</span><span class="p">[:]</span>
<span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">9</span><span class="p">,</span> <span class="mi">16</span><span class="p">,</span> <span class="mi">25</span><span class="p">]</span>
</pre></div>
<p>列表还支持连接：</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">squares</span> <span class="o">+</span> <span class="p">[</span><span class="mi">36</span><span class="p">,</span> <span class="mi">49</span><span class="p">,</span> <span class="mi">64</span><span class="p">,</span> <span class="mi">81</span><span class="p">,</span> <span class="mi">100</span><span class="p">]</span>
<span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">9</span><span class="p">,</span> <span class="mi">16</span><span class="p">,</span> <span class="mi">25</span><span class="p">,</span> <span class="mi">36</span><span class="p">,</span> <span class="mi">49</span><span class="p">,</span> <span class="mi">64</span><span class="p">,</span> <span class="mi">81</span><span class="p">,</span> <span class="mi">100</span><span class="p">]</span>
</pre></div>
<p>字符串是不可改变的,列表是可变的。</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">cubes</span> <span class="o">=</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">8</span><span class="p">,</span> <span class="mi">27</span><span class="p">,</span> <span class="mi">65</span><span class="p">,</span> <span class="mi">125</span><span class="p">]</span> <span class="c1"># something's wrong here</span>
<span class="o">>>></span> <span class="mi">4</span> <span class="o">**</span> <span class="mi">3</span> <span class="c1"># the cube of 4 is 64, not 65!</span>
<span class="mi">64</span>
<span class="o">>>></span> <span class="n">cubes</span><span class="p">[</span><span class="mi">3</span><span class="p">]</span> <span class="o">=</span> <span class="mi">64</span> <span class="c1"># replace the wrong value</span>
<span class="o">>>></span> <span class="n">cubes</span>
<span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">8</span><span class="p">,</span> <span class="mi">27</span><span class="p">,</span> <span class="mi">64</span><span class="p">,</span> <span class="mi">125</span><span class="p">]</span>
</pre></div>
<p>append()方法可以添加元素到尾部：</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">cubes</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="mi">216</span><span class="p">)</span> <span class="c1"># add the cube of 6</span>
<span class="o">>>></span> <span class="n">cubes</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="mi">7</span> <span class="o">**</span> <span class="mi">3</span><span class="p">)</span> <span class="c1"># and the cube of 7</span>
<span class="o">>>></span> <span class="n">cubes</span>
<span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">8</span><span class="p">,</span> <span class="mi">27</span><span class="p">,</span> <span class="mi">64</span><span class="p">,</span> <span class="mi">125</span><span class="p">,</span> <span class="mi">216</span><span class="p">,</span> <span class="mi">343</span><span class="p">]</span>
</pre></div>
<p>也可以对切片赋值，此操作甚至可以改变列表的尺寸，或清空它:</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">letters</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="s1">'e'</span><span class="p">,</span> <span class="s1">'f'</span><span class="p">,</span> <span class="s1">'g'</span><span class="p">]</span>
<span class="o">>>></span> <span class="n">letters</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="s1">'e'</span><span class="p">,</span> <span class="s1">'f'</span><span class="p">,</span> <span class="s1">'g'</span><span class="p">]</span>
<span class="o">>>></span> <span class="c1"># replace some values</span>
<span class="o">>>></span> <span class="n">letters</span><span class="p">[</span><span class="mi">2</span><span class="p">:</span><span class="mi">5</span><span class="p">]</span> <span class="o">=</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="s1">'E'</span><span class="p">]</span>
<span class="o">>>></span> <span class="n">letters</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="s1">'E'</span><span class="p">,</span> <span class="s1">'f'</span><span class="p">,</span> <span class="s1">'g'</span><span class="p">]</span>
<span class="o">>>></span> <span class="c1"># now remove them</span>
<span class="o">>>></span> <span class="n">letters</span><span class="p">[</span><span class="mi">2</span><span class="p">:</span><span class="mi">5</span><span class="p">]</span> <span class="o">=</span> <span class="p">[]</span>
<span class="o">>>></span> <span class="n">letters</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">'f'</span><span class="p">,</span> <span class="s1">'g'</span><span class="p">]</span>
<span class="o">>>></span> <span class="c1"># clear the list by replacing all the elements with an empty list</span>
<span class="o">>>></span> <span class="n">letters</span><span class="p">[:]</span> <span class="o">=</span> <span class="p">[]</span>
<span class="o">>>></span> <span class="n">letters</span>
<span class="p">[]</span>
</pre></div>
<p>内置函数 len() 同样适用于列表:</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">letters</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="o">>>></span> <span class="nb">len</span><span class="p">(</span><span class="n">letters</span><span class="p">)</span>
<span class="mi">4</span>
</pre></div>
<p>支持嵌套列表(包含其它列表的列表)，例如:</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">a</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="o">>>></span> <span class="n">n</span> <span class="o">=</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">]</span>
<span class="o">>>></span> <span class="n">x</span> <span class="o">=</span> <span class="p">[</span><span class="n">a</span><span class="p">,</span> <span class="n">n</span><span class="p">]</span>
<span class="o">>>></span> <span class="n">x</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="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">]]</span>
<span class="o">>>></span> <span class="n">x</span><span class="p">[</span><span class="mi">0</span><span class="p">]</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="o">>>></span> <span class="n">x</span><span class="p">[</span><span class="mi">0</span><span class="p">][</span><span class="mi">1</span><span class="p">]</span>
<span class="s1">'b'</span>
</pre></div>
<h2 id="_2">深入列表</h2>
<p>列表的所有方法如下： </p>
<p>方法 | 功能
| --- | --- |
list.append(x) |附加元素到列表末端，相当于a[len(a):] = [x]。<br>
list.extend(L) |附加列表L的内容到当前列表后面，相当于 a[len(a):] = L 。<br>
list.insert(i, x) |在指定位置i插入x。i表示插入位置，原来的i位置如果有元素则往后移动一个位置，例如 a.insert(0, x)会插入到列表首部，而a.insert(len(a), x)相当于a.append(x)。<br>
list.remove(x) |删除列表中第一个值为x的元素。如果没有就报错。<br>
list.pop([i]) |删除列表指定位置的元素，并将其返回该元素。如果没有指定索引针对最后一个元素。方括号表示i是可选的。<br>
list.clear() |从列表中删除所有元素。相当于 del a[:]
list.index(x[, start[, end]]) |返回第一个值为x的元素的索引。如果没有则报错。<br>
list.count(x) |返回x在列表中出现的次数。<br>
list.sort(cmp=None, key=None, reverse=False) |就地对列表中的元素进行排序。<br>
list.reverse() |就地反转元素。<br>
list.copy() |返回列表的浅拷贝。等同于 a[:]。</p>
<p>实例： </p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">fruits</span> <span class="o">=</span> <span class="p">[</span><span class="s1">'orange'</span><span class="p">,</span> <span class="s1">'apple'</span><span class="p">,</span> <span class="s1">'pear'</span><span class="p">,</span> <span class="s1">'banana'</span><span class="p">,</span> <span class="s1">'kiwi'</span><span class="p">,</span> <span class="s1">'apple'</span><span class="p">,</span> <span class="s1">'banana'</span><span class="p">]</span>
<span class="o">>>></span> <span class="n">fruits</span><span class="o">.</span><span class="n">count</span><span class="p">(</span><span class="s1">'apple'</span><span class="p">)</span>
<span class="mi">2</span>
<span class="o">>>></span> <span class="n">fruits</span><span class="o">.</span><span class="n">count</span><span class="p">(</span><span class="s1">'tangerine'</span><span class="p">)</span>
<span class="mi">0</span>
<span class="o">>>></span> <span class="n">fruits</span><span class="o">.</span><span class="n">index</span><span class="p">(</span><span class="s1">'banana'</span><span class="p">)</span>
<span class="mi">3</span>
<span class="o">>>></span> <span class="n">fruits</span><span class="o">.</span><span class="n">index</span><span class="p">(</span><span class="s1">'banana'</span><span class="p">,</span> <span class="mi">4</span><span class="p">)</span> <span class="c1"># Find next banana starting a position 4</span>
<span class="mi">6</span>
<span class="o">>>></span> <span class="n">fruits</span><span class="o">.</span><span class="n">reverse</span><span class="p">()</span>
<span class="o">>>></span> <span class="n">fruits</span>
<span class="p">[</span><span class="s1">'banana'</span><span class="p">,</span> <span class="s1">'apple'</span><span class="p">,</span> <span class="s1">'kiwi'</span><span class="p">,</span> <span class="s1">'banana'</span><span class="p">,</span> <span class="s1">'pear'</span><span class="p">,</span> <span class="s1">'apple'</span><span class="p">,</span> <span class="s1">'orange'</span><span class="p">]</span>
<span class="o">>>></span> <span class="n">fruits</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="s1">'grape'</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">fruits</span>
<span class="p">[</span><span class="s1">'banana'</span><span class="p">,</span> <span class="s1">'apple'</span><span class="p">,</span> <span class="s1">'kiwi'</span><span class="p">,</span> <span class="s1">'banana'</span><span class="p">,</span> <span class="s1">'pear'</span><span class="p">,</span> <span class="s1">'apple'</span><span class="p">,</span> <span class="s1">'orange'</span><span class="p">,</span> <span class="s1">'grape'</span><span class="p">]</span>
<span class="o">>>></span> <span class="n">fruits</span><span class="o">.</span><span class="n">sort</span><span class="p">()</span>
<span class="o">>>></span> <span class="n">fruits</span>
<span class="p">[</span><span class="s1">'apple'</span><span class="p">,</span> <span class="s1">'apple'</span><span class="p">,</span> <span class="s1">'banana'</span><span class="p">,</span> <span class="s1">'banana'</span><span class="p">,</span> <span class="s1">'grape'</span><span class="p">,</span> <span class="s1">'kiwi'</span><span class="p">,</span> <span class="s1">'orange'</span><span class="p">,</span> <span class="s1">'pear'</span><span class="p">]</span>
<span class="o">>>></span> <span class="n">fruits</span><span class="o">.</span><span class="n">pop</span><span class="p">()</span>
<span class="s1">'pear'</span>
</pre></div>
<p>也许大家会发现像insert、remove或者 sort这些修改列表的方法没有打印返回值–它们返回 <code>None</code>。 <a href="https://docs.python.org/3/tutorial/datastructures.html#id3">参考</a>。 这是所有可变的数据类型的统一的设计原则。</p>
<ul>
<li>把链表当作堆栈使用</li>
</ul>
<p>堆栈后进先出。进使用append()，出使用pop()。例如: </p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">stack</span> <span class="o">=</span> <span class="p">[</span><span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">]</span>
<span class="o">>>></span> <span class="n">stack</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="mi">6</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">stack</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="mi">7</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">stack</span>
<span class="p">[</span><span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">6</span><span class="p">,</span> <span class="mi">7</span><span class="p">]</span>
<span class="o">>>></span> <span class="n">stack</span><span class="o">.</span><span class="n">pop</span><span class="p">()</span>
<span class="mi">7</span>
<span class="o">>>></span> <span class="n">stack</span>
<span class="p">[</span><span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">6</span><span class="p">]</span>
<span class="o">>>></span> <span class="n">stack</span><span class="o">.</span><span class="n">pop</span><span class="p">()</span>
<span class="mi">6</span>
<span class="o">>>></span> <span class="n">stack</span><span class="o">.</span><span class="n">pop</span><span class="p">()</span>
<span class="mi">5</span>
<span class="o">>>></span> <span class="n">stack</span>
<span class="p">[</span><span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">]</span>
</pre></div>
<ul>
<li>把列表当作队列使用</li>
</ul>
<p>列表先进先出。列表头部插入或者删除元素的效率并不高，因为其他相关元素需要移动，建议使用collections.deque。 </p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="kn">from</span> <span class="nn">collections</span> <span class="kn">import</span> <span class="n">deque</span>
<span class="o">>>></span> <span class="n">queue</span> <span class="o">=</span> <span class="n">deque</span><span class="p">([</span><span class="s2">"Eric"</span><span class="p">,</span> <span class="s2">"John"</span><span class="p">,</span> <span class="s2">"Michael"</span><span class="p">])</span>
<span class="o">>>></span> <span class="n">queue</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="s2">"Terry"</span><span class="p">)</span> <span class="c1"># Terry arrives</span>
<span class="o">>>></span> <span class="n">queue</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="s2">"Graham"</span><span class="p">)</span> <span class="c1"># Graham arrives</span>
<span class="o">>>></span> <span class="n">queue</span><span class="o">.</span><span class="n">popleft</span><span class="p">()</span> <span class="c1"># The first to arrive now leaves</span>
<span class="s1">'Eric'</span>
<span class="o">>>></span> <span class="n">queue</span><span class="o">.</span><span class="n">popleft</span><span class="p">()</span> <span class="c1"># The second to arrive now leaves</span>
<span class="s1">'John'</span>
<span class="o">>>></span> <span class="n">queue</span> <span class="c1"># Remaining queue in order of arrival</span>
<span class="n">deque</span><span class="p">([</span><span class="s1">'Michael'</span><span class="p">,</span> <span class="s1">'Terry'</span><span class="p">,</span> <span class="s1">'Graham'</span><span class="p">])</span>
</pre></div>
<h2 id="_3">列表推导式</h2>
<p>列表推导(表达)式可以快捷地创建列表。用于基于列表元素(可以附加条件)创建列表。 </p>
<p>传统方式: </p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">squares</span> <span class="o">=</span> <span class="p">[]</span>
<span class="o">>>></span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">10</span><span class="p">):</span>
<span class="o">...</span> <span class="n">squares</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">x</span><span class="o">**</span><span class="mi">2</span><span class="p">)</span>
<span class="o">...</span>
<span class="o">>>></span> <span class="n">squares</span>
<span class="p">[</span><span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">9</span><span class="p">,</span> <span class="mi">16</span><span class="p">,</span> <span class="mi">25</span><span class="p">,</span> <span class="mi">36</span><span class="p">,</span> <span class="mi">49</span><span class="p">,</span> <span class="mi">64</span><span class="p">,</span> <span class="mi">81</span><span class="p">]</span>
</pre></div>
<p>列表推导: </p>
<div class="highlight"><pre><span></span><span class="n">squares</span> <span class="o">=</span> <span class="p">[</span><span class="n">x</span><span class="o">**</span><span class="mi">2</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">10</span><span class="p">)]</span>
</pre></div>
<p>等价于 squares = map(lambda x: x**2, range(10))，但可读性更好、更简洁。 </p>
<p>列表推导式包含在放括号中，表达式后有for子句，之后可以有零或多个 for 或 if 子句。结果是基于表达式计算出来的列表:</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="p">[(</span><span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">)</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">]</span> <span class="k">for</span> <span class="n">y</span> <span class="ow">in</span> <span class="p">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">4</span><span class="p">]</span> <span class="k">if</span> <span class="n">x</span> <span class="o">!=</span> <span class="n">y</span><span class="p">]</span>
<span class="p">[(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">3</span><span class="p">),</span> <span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">4</span><span class="p">),</span> <span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">),</span> <span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">1</span><span class="p">),</span> <span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">4</span><span class="p">),</span> <span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">1</span><span class="p">),</span> <span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">)]</span>
</pre></div>
<p>等同于: </p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">combs</span> <span class="o">=</span> <span class="p">[]</span>
<span class="o">>>></span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">]:</span>
<span class="o">...</span> <span class="k">for</span> <span class="n">y</span> <span class="ow">in</span> <span class="p">[</span><span class="mi">3</span><span class="p">,</span><span class="mi">1</span><span class="p">,</span><span class="mi">4</span><span class="p">]:</span>
<span class="o">...</span> <span class="k">if</span> <span class="n">x</span> <span class="o">!=</span> <span class="n">y</span><span class="p">:</span>
<span class="o">...</span> <span class="n">combs</span><span class="o">.</span><span class="n">append</span><span class="p">((</span><span class="n">x</span><span class="p">,</span> <span class="n">y</span><span class="p">))</span>
<span class="o">...</span>
<span class="o">>>></span> <span class="n">combs</span>
<span class="p">[(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">3</span><span class="p">),</span> <span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">4</span><span class="p">),</span> <span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">),</span> <span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">1</span><span class="p">),</span> <span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">4</span><span class="p">),</span> <span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">1</span><span class="p">),</span> <span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">)]</span>
</pre></div>
<p>如果想要得到元组 (例如，上例的 (x, y))，必须在表达式要加上括号:</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">vec</span> <span class="o">=</span> <span class="p">[</span><span class="o">-</span><span class="mi">4</span><span class="p">,</span> <span class="o">-</span><span class="mi">2</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">4</span><span class="p">]</span>
<span class="o">>>></span> <span class="c1"># create a new list with the values doubled</span>
<span class="o">>>></span> <span class="p">[</span><span class="n">x</span><span class="o">*</span><span class="mi">2</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">vec</span><span class="p">]</span>
<span class="p">[</span><span class="o">-</span><span class="mi">8</span><span class="p">,</span> <span class="o">-</span><span class="mi">4</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">8</span><span class="p">]</span>
<span class="o">>>></span> <span class="c1"># filter the list to exclude negative numbers</span>
<span class="o">>>></span> <span class="p">[</span><span class="n">x</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">vec</span> <span class="k">if</span> <span class="n">x</span> <span class="o">>=</span> <span class="mi">0</span><span class="p">]</span>
<span class="p">[</span><span class="mi">0</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">4</span><span class="p">]</span>
<span class="o">>>></span> <span class="c1"># apply a function to all the elements</span>
<span class="o">>>></span> <span class="p">[</span><span class="nb">abs</span><span class="p">(</span><span class="n">x</span><span class="p">)</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="n">vec</span><span class="p">]</span>
<span class="p">[</span><span class="mi">4</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">4</span><span class="p">]</span>
<span class="o">>>></span> <span class="c1"># call a method on each element</span>
<span class="o">>>></span> <span class="n">freshfruit</span> <span class="o">=</span> <span class="p">[</span><span class="s1">' banana'</span><span class="p">,</span> <span class="s1">' loganberry '</span><span class="p">,</span> <span class="s1">'passion fruit '</span><span class="p">]</span>
<span class="o">>>></span> <span class="p">[</span><span class="n">weapon</span><span class="o">.</span><span class="n">strip</span><span class="p">()</span> <span class="k">for</span> <span class="n">weapon</span> <span class="ow">in</span> <span class="n">freshfruit</span><span class="p">]</span>
<span class="p">[</span><span class="s1">'banana'</span><span class="p">,</span> <span class="s1">'loganberry'</span><span class="p">,</span> <span class="s1">'passion fruit'</span><span class="p">]</span>
<span class="o">>>></span> <span class="c1"># create a list of 2-tuples like (number, square)</span>
<span class="o">>>></span> <span class="p">[(</span><span class="n">x</span><span class="p">,</span> <span class="n">x</span><span class="o">**</span><span class="mi">2</span><span class="p">)</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">6</span><span class="p">)]</span>
<span class="p">[(</span><span class="mi">0</span><span class="p">,</span> <span class="mi">0</span><span class="p">),</span> <span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">1</span><span class="p">),</span> <span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">4</span><span class="p">),</span> <span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">9</span><span class="p">),</span> <span class="p">(</span><span class="mi">4</span><span class="p">,</span> <span class="mi">16</span><span class="p">),</span> <span class="p">(</span><span class="mi">5</span><span class="p">,</span> <span class="mi">25</span><span class="p">)]</span>
<span class="o">>>></span> <span class="c1"># the tuple must be parenthesized, otherwise an error is raised</span>
<span class="o">>>></span> <span class="p">[</span><span class="n">x</span><span class="p">,</span> <span class="n">x</span><span class="o">**</span><span class="mi">2</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">6</span><span class="p">)]</span>
<span class="n">File</span> <span class="s2">"<stdin>"</span><span class="p">,</span> <span class="n">line</span> <span class="mi">1</span><span class="p">,</span> <span class="ow">in</span> <span class="err">?</span>
<span class="p">[</span><span class="n">x</span><span class="p">,</span> <span class="n">x</span><span class="o">**</span><span class="mi">2</span> <span class="k">for</span> <span class="n">x</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">6</span><span class="p">)]</span>
<span class="o">^</span>
<span class="ne">SyntaxError</span><span class="p">:</span> <span class="n">invalid</span> <span class="n">syntax</span>
<span class="o">>>></span> <span class="c1"># flatten a list using a listcomp with two 'for'</span>
<span class="o">>>></span> <span class="n">vec</span> <span class="o">=</span> <span class="p">[[</span><span class="mi">1</span><span class="p">,</span><span class="mi">2</span><span class="p">,</span><span class="mi">3</span><span class="p">],</span> <span class="p">[</span><span class="mi">4</span><span class="p">,</span><span class="mi">5</span><span class="p">,</span><span class="mi">6</span><span class="p">],</span> <span class="p">[</span><span class="mi">7</span><span class="p">,</span><span class="mi">8</span><span class="p">,</span><span class="mi">9</span><span class="p">]]</span>
<span class="o">>>></span> <span class="p">[</span><span class="n">num</span> <span class="k">for</span> <span class="n">elem</span> <span class="ow">in</span> <span class="n">vec</span> <span class="k">for</span> <span class="n">num</span> <span class="ow">in</span> <span class="n">elem</span><span class="p">]</span>
<span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">6</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">8</span><span class="p">,</span> <span class="mi">9</span><span class="p">]</span>
</pre></div>
<p>列表推导式可使用复杂的表达式和嵌套函数:</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="kn">from</span> <span class="nn">math</span> <span class="kn">import</span> <span class="n">pi</span>
<span class="o">>>></span> <span class="p">[</span><span class="nb">str</span><span class="p">(</span><span class="nb">round</span><span class="p">(</span><span class="n">pi</span><span class="p">,</span> <span class="n">i</span><span class="p">))</span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">6</span><span class="p">)]</span>
<span class="p">[</span><span class="s1">'3.1'</span><span class="p">,</span> <span class="s1">'3.14'</span><span class="p">,</span> <span class="s1">'3.142'</span><span class="p">,</span> <span class="s1">'3.1416'</span><span class="p">,</span> <span class="s1">'3.14159'</span><span class="p">]</span>
</pre></div>
<ul>
<li>嵌套列表推导式</li>
</ul>
<p>有如下嵌套列表: </p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">matrix</span> <span class="o">=</span> <span class="p">[</span>
<span class="o">...</span> <span class="p">[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="mi">3</span><span class="p">,</span> <span class="mi">4</span><span class="p">],</span>
<span class="o">...</span> <span class="p">[</span><span class="mi">5</span><span class="p">,</span> <span class="mi">6</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">8</span><span class="p">],</span>
<span class="o">...</span> <span class="p">[</span><span class="mi">9</span><span class="p">,</span> <span class="mi">10</span><span class="p">,</span> <span class="mi">11</span><span class="p">,</span> <span class="mi">12</span><span class="p">],</span>
<span class="o">...</span> <span class="p">]</span>
</pre></div>
<p>交换行和列: </p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="p">[[</span><span class="n">row</span><span class="p">[</span><span class="n">i</span><span class="p">]</span> <span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">matrix</span><span class="p">]</span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">4</span><span class="p">)]</span>
<span class="p">[[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">9</span><span class="p">],</span> <span class="p">[</span><span class="mi">2</span><span class="p">,</span> <span class="mi">6</span><span class="p">,</span> <span class="mi">10</span><span class="p">],</span> <span class="p">[</span><span class="mi">3</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">11</span><span class="p">],</span> <span class="p">[</span><span class="mi">4</span><span class="p">,</span> <span class="mi">8</span><span class="p">,</span> <span class="mi">12</span><span class="p">]]</span>
</pre></div>
<p>等同于:</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">transposed</span> <span class="o">=</span> <span class="p">[]</span>
<span class="o">>>></span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">4</span><span class="p">):</span>
<span class="o">...</span> <span class="n">transposed</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="n">i</span><span class="p">]</span> <span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">matrix</span><span class="p">])</span>
<span class="o">...</span>
<span class="o">>>></span> <span class="n">transposed</span>
<span class="p">[[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">9</span><span class="p">],</span> <span class="p">[</span><span class="mi">2</span><span class="p">,</span> <span class="mi">6</span><span class="p">,</span> <span class="mi">10</span><span class="p">],</span> <span class="p">[</span><span class="mi">3</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">11</span><span class="p">],</span> <span class="p">[</span><span class="mi">4</span><span class="p">,</span> <span class="mi">8</span><span class="p">,</span> <span class="mi">12</span><span class="p">]]</span>
</pre></div>
<p>也等同于: </p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">transposed</span> <span class="o">=</span> <span class="p">[]</span>
<span class="o">>>></span> <span class="k">for</span> <span class="n">i</span> <span class="ow">in</span> <span class="nb">range</span><span class="p">(</span><span class="mi">4</span><span class="p">):</span>
<span class="o">...</span> <span class="c1"># the following 3 lines implement the nested listcomp</span>
<span class="o">...</span> <span class="n">transposed_row</span> <span class="o">=</span> <span class="p">[]</span>
<span class="o">...</span> <span class="k">for</span> <span class="n">row</span> <span class="ow">in</span> <span class="n">matrix</span><span class="p">:</span>
<span class="o">...</span> <span class="n">transposed_row</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="n">i</span><span class="p">])</span>
<span class="o">...</span> <span class="n">transposed</span><span class="o">.</span><span class="n">append</span><span class="p">(</span><span class="n">transposed_row</span><span class="p">)</span>
<span class="o">...</span>
<span class="o">>>></span> <span class="n">transposed</span>
<span class="p">[[</span><span class="mi">1</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">9</span><span class="p">],</span> <span class="p">[</span><span class="mi">2</span><span class="p">,</span> <span class="mi">6</span><span class="p">,</span> <span class="mi">10</span><span class="p">],</span> <span class="p">[</span><span class="mi">3</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">11</span><span class="p">],</span> <span class="p">[</span><span class="mi">4</span><span class="p">,</span> <span class="mi">8</span><span class="p">,</span> <span class="mi">12</span><span class="p">]]</span>
</pre></div>
<p>zip()内置函数更好: </p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="nb">list</span><span class="p">(</span><span class="nb">zip</span><span class="p">(</span><span class="o">*</span><span class="n">matrix</span><span class="p">))</span>
<span class="p">[(</span><span class="mi">1</span><span class="p">,</span> <span class="mi">5</span><span class="p">,</span> <span class="mi">9</span><span class="p">),</span> <span class="p">(</span><span class="mi">2</span><span class="p">,</span> <span class="mi">6</span><span class="p">,</span> <span class="mi">10</span><span class="p">),</span> <span class="p">(</span><span class="mi">3</span><span class="p">,</span> <span class="mi">7</span><span class="p">,</span> <span class="mi">11</span><span class="p">),</span> <span class="p">(</span><span class="mi">4</span><span class="p">,</span> <span class="mi">8</span><span class="p">,</span> <span class="mi">12</span><span class="p">)]</span>
</pre></div>
<ul>
<li>小结：创建列表的常用方法：</li>
</ul>
<p>1，中括号：比如data = [4, 9, 2, 8, 3, 2, 5, 4, 2]
2，range：比如list(range(100))
3, 列表推导式：比如[expression for variable in sequence]，实际是中括号的变种。</p>
<p>列表相关的内置函数len、max、min、sum、sorted、list，请在内置函数中学习。后面的习题会覆盖这些函数。</p>
<h2 id="_4">参考资料</h2>
<ul>
<li>python测试等IT技术支持qq群： 144081101(后期会录制视频存在该群群文件) 591302926 567351477 钉钉免费群：21745728</li>
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<li><a href="https://china-testing.github.io/python3_crash7.html">本文最新版本地址</a></li>
<li><a href="https://github.com/china-testing/python-api-tesing">本文涉及的python测试开发库</a> 谢谢点赞！</li>
<li><a href="https://github.com/china-testing/python-api-tesing/blob/master/books.md">本文相关海量书籍下载</a></li>
<li><a href="https://china-testing.github.io/testing_training.html">接口自动化性能测试线上培训大纲</a></li>
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<li><a href="http://blog.sciencenet.cn/blog-2604609-1112306.html">pandas数据分析scrapy爬虫 521070358 Py人工智能pandas-opencv 6089740</a></li>
<li><a href="http://blog.sciencenet.cn/blog-2604609-1112306.html">中医解梦看相八字算命qq群 391441566 csdn书籍下载-python爬虫 437355848</a></li>
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