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<title>[雪峰磁针石博客]python3快速入门教程2数据结构2字符串</title>
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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2字符串">[雪峰磁针石博客]python3快速入门教程2数据结构2字符串</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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<address class="vcard author">
By <a class="url fn" href="/author/andrew.html">andrew</a>
</address>
<p>In <a href="/category/python.html">python</a>.</p>
</footer><!-- /.post-info --> <h2 id="_1">快速入门</h2>
<p>字符串可以包含在单引号或双引号中。</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="s1">'spam eggs'</span> <span class="c1"># single quotes</span>
<span class="s1">'spam eggs'</span>
<span class="o">>>></span> <span class="s1">'doesn</span><span class="se">\'</span><span class="s1">t'</span> <span class="c1"># use \' to escape the single quote...</span>
<span class="s2">"doesn't"</span>
<span class="o">>>></span> <span class="s2">"doesn't"</span> <span class="c1"># ...or use double quotes instead</span>
<span class="s2">"doesn't"</span>
<span class="o">>>></span> <span class="s1">'"Yes," he said.'</span>
<span class="s1">'"Yes," he said.'</span>
<span class="o">>>></span> <span class="s2">"</span><span class="se">\"</span><span class="s2">Yes,</span><span class="se">\"</span><span class="s2"> he said."</span>
<span class="s1">'"Yes," he said.'</span>
<span class="o">>>></span> <span class="s1">'"Isn</span><span class="se">\'</span><span class="s1">t," she said.'</span>
<span class="s1">'"Isn</span><span class="se">\'</span><span class="s1">t," she said.'</span>
</pre></div>
<p>解释器按照字符串被输入的方式显示字符串，通常包含在单引号中，如果内容包含包含单引号，则包含在双引号中。</p>
<p>print会以更可视的格式显示：</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="s1">'"Isn</span><span class="se">\'</span><span class="s1">t," she said.'</span>
<span class="s1">'"Isn</span><span class="se">\'</span><span class="s1">t," she said.'</span>
<span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="s1">'"Isn</span><span class="se">\'</span><span class="s1">t," she said.'</span><span class="p">)</span>
<span class="s2">"Isn't,"</span> <span class="n">she</span> <span class="n">said</span><span class="o">.</span>
<span class="o">>>></span> <span class="n">s</span> <span class="o">=</span> <span class="s1">'First line.</span><span class="se">\n</span><span class="s1">Second line.'</span> <span class="c1"># \n means newline</span>
<span class="o">>>></span> <span class="n">s</span> <span class="c1"># without print(), \n is included in the output</span>
<span class="s1">'First line.</span><span class="se">\n</span><span class="s1">Second line.'</span>
<span class="o">>>></span> <span class="k">print</span><span class="p">(</span><span class="n">s</span><span class="p">)</span> <span class="c1"># with print(), \n produces a new line</span>
<span class="n">First</span> <span class="n">line</span><span class="o">.</span>
<span class="n">Second</span> <span class="n">line</span><span class="o">.</span>
</pre></div>
<p>字符串前面添加'r'表示原始字符串，里面的反斜杠不会转义：</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="sa">r</span><span class="s1">'C:\Program Files\foo\bar</span><span class="se">\'</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="sa">r</span><span class="s1">'C:\Program Files\foo\bar</span><span class="se">\'</span>
<span class="o">^</span>
<span class="ne">SyntaxError</span><span class="p">:</span> <span class="n">EOL</span> <span class="k">while</span> <span class="n">scanning</span> <span class="n">string</span> <span class="n">literal</span>
<span class="o">>>></span> <span class="sa">r</span><span class="s1">'C:\Program Files\foo\bar''</span><span class="se">\\</span><span class="s1">'</span>
<span class="s1">'C:</span><span class="se">\\</span><span class="s1">Program Files</span><span class="se">\\</span><span class="s1">foo</span><span class="se">\\</span><span class="s1">bar</span><span class="se">\\</span><span class="s1">'</span>
<span class="o">>>></span>
</pre></div>
<p>原始字符串不能以单个反斜杠结尾。换而言之，原始字符串的最后一个字符不能是反斜杠，除非你对其进行转义（但进行转义时，用于转义的反斜杠也将是字符串的一部分）如果最后一个字符（位于结束引号前面的那个字符）为反斜杠，且未对其进行转义，Python将无法判断字符串是否到此结束。</p>
<p>跨行的字符串多使用三引号，即三个单引号或者三个双引号：</p>
<div class="highlight"><pre><span></span><span class="k">print</span><span class="p">(</span><span class="s2">"""</span><span class="se">\</span>
<span class="s2">Usage: thingy [OPTIONS]</span>
<span class="s2"> -h Display this usage message</span>
<span class="s2"> -H hostname Hostname to connect to</span>
<span class="s2">"""</span><span class="p">)</span>
<span class="n">Usage</span><span class="p">:</span> <span class="n">thingy</span> <span class="p">[</span><span class="n">OPTIONS</span><span class="p">]</span>
<span class="o">-</span><span class="n">h</span> <span class="n">Display</span> <span class="n">this</span> <span class="n">usage</span> <span class="n">message</span>
<span class="o">-</span><span class="n">H</span> <span class="n">hostname</span> <span class="n">Hostname</span> <span class="n">to</span> <span class="n">connect</span> <span class="n">to</span>
</pre></div>
<p>注意第一个三引号后面有反斜杠，就不会输出第一个换行符。末尾的反斜杠表示续行。</p>
<p>字符串可用+操作符连接，用*重复:</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="mi">3</span> <span class="o">*</span> <span class="s1">'un'</span> <span class="o">+</span> <span class="s1">'ium'</span>
<span class="s1">'unununium'</span>
</pre></div>
<p>相邻字符串文本会自动连接，它只用于字符串文本，不能用于字符串表达式和变量(需要使用加号)等：</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="s1">'Py'</span> <span class="s1">'thon'</span>
<span class="s1">'Python'</span>
<span class="o">>>></span> <span class="n">prefix</span> <span class="s1">'thon</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="n">prefix</span> <span class="s1">'thon</span>
<span class="o">^</span>
<span class="ne">SyntaxError</span><span class="p">:</span> <span class="n">EOL</span> <span class="k">while</span> <span class="n">scanning</span> <span class="n">string</span> <span class="n">literal</span>
<span class="o">>>></span> <span class="p">(</span><span class="s1">'un'</span> <span class="o">*</span> <span class="mi">3</span><span class="p">)</span> <span class="s1">'ium'</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="s1">'un'</span> <span class="o">*</span> <span class="mi">3</span><span class="p">)</span> <span class="s1">'ium'</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="n">prefix</span> <span class="o">+</span> <span class="s1">'thon'</span>
<span class="s1">'Python'</span>
<span class="c1"># 在拆分长字符串时很有用。</span>
<span class="o">>>></span> <span class="n">text</span> <span class="o">=</span> <span class="p">(</span><span class="s1">'Put several strings within parentheses '</span>
<span class="o">...</span> <span class="s1">'to have them joined together.'</span><span class="p">)</span>
<span class="o">>>></span> <span class="n">text</span>
<span class="s1">'Put several strings within parentheses to have them joined together.'</span>
</pre></div>
<p>字符串下标又称索引和C类似 ，第一个字符索引为 0 。没有独立的字符类型，字符就是长度为 1 的字符串，也可以使用负数，-1表示倒数第一个，-2表示倒数第二个，以此类推。不存在的下标会报IndexError。</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">word</span> <span class="o">=</span> <span class="s1">'Python'</span>
<span class="o">>>></span> <span class="n">word</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="c1"># character in position 0</span>
<span class="s1">'P'</span>
<span class="o">>>></span> <span class="n">word</span><span class="p">[</span><span class="mi">5</span><span class="p">]</span> <span class="c1"># character in position 5</span>
<span class="s1">'n'</span>
<span class="o">>>></span> <span class="n">word</span><span class="p">[</span><span class="o">-</span><span class="mi">1</span><span class="p">]</span> <span class="c1"># last character</span>
<span class="s1">'n'</span>
<span class="o">>>></span> <span class="n">word</span><span class="p">[</span><span class="o">-</span><span class="mi">2</span><span class="p">]</span> <span class="c1"># second-last character</span>
<span class="s1">'o'</span>
<span class="o">>>></span> <span class="n">word</span><span class="p">[</span><span class="o">-</span><span class="mi">6</span><span class="p">]</span>
<span class="s1">'P'</span>
<span class="o">>>></span> <span class="n">word</span><span class="p">[</span><span class="o">-</span><span class="mi">16</span><span class="p">]</span>
<span class="n">Traceback</span> <span class="p">(</span><span class="n">most</span> <span class="n">recent</span> <span class="n">call</span> <span class="n">last</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="o"><</span><span class="n">module</span><span class="o">></span>
<span class="ne">IndexError</span><span class="p">:</span> <span class="n">string</span> <span class="n">index</span> <span class="n">out</span> <span class="n">of</span> <span class="nb">range</span>
<span class="o">>>></span> <span class="n">word</span><span class="p">[</span><span class="mi">16</span><span class="p">]</span>
<span class="n">Traceback</span> <span class="p">(</span><span class="n">most</span> <span class="n">recent</span> <span class="n">call</span> <span class="n">last</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="o"><</span><span class="n">module</span><span class="o">></span>
<span class="ne">IndexError</span><span class="p">:</span> <span class="n">string</span> <span class="n">index</span> <span class="n">out</span> <span class="n">of</span> <span class="nb">range</span>
</pre></div>
<p>字符串支持切片：由两个索引，中间是冒号。第一个索引表示起点，包含该元素，默认为0；第2个索引表示终点，不包含该元素，默认为字符串末尾。s[:i] + s[i:]等同于s。</p>
<div class="highlight"><pre><span></span><span class="o">>>></span> <span class="n">word</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="c1"># characters from position 0 (included) to 2 (excluded)</span>
<span class="s1">'Py'</span>
<span class="o">>>></span> <span class="n">word</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="c1"># characters from position 2 (included) to 5 (excluded)</span>
<span class="s1">'tho'</span>
<span class="o">>>></span> <span class="n">word</span><span class="p">[:</span><span class="mi">2</span><span class="p">]</span> <span class="o">+</span> <span class="n">word</span><span class="p">[</span><span class="mi">2</span><span class="p">:]</span>
<span class="s1">'Python'</span>
<span class="o">>>></span> <span class="n">word</span><span class="p">[:</span><span class="mi">4</span><span class="p">]</span> <span class="o">+</span> <span class="n">word</span><span class="p">[</span><span class="mi">4</span><span class="p">:]</span>
<span class="s1">'Python'</span>
<span class="o">>>></span> <span class="n">word</span><span class="p">[:</span><span class="mi">2</span><span class="p">]</span> <span class="c1"># character from the beginning to position 2 (excluded)</span>
<span class="s1">'Py'</span>
<span class="o">>>></span> <span class="n">word</span><span class="p">[</span><span class="mi">4</span><span class="p">:]</span> <span class="c1"># characters from position 4 (included) to the end</span>
<span class="s1">'on'</span>
<span class="o">>>></span> <span class="n">word</span><span class="p">[</span><span class="o">-</span><span class="mi">2</span><span class="p">:]</span> <span class="c1"># characters from the second-last (included) to the end</span>
<span class="s1">'on'</span>
</pre></div>
<p>记住切片的工作方式：切片索引是在字符之间。左边第一个字符的索引为0，右界索引为字符串长度n 。例如:</p>
<div class="highlight"><pre><span></span> <span class="o">+---+---+---+---+---+---+</span>
<span class="o">|</span> <span class="n">P</span> <span class="o">|</span> <span class="n">y</span> <span class="o">|</span> <span class="n">t</span> <span class="o">|</span> <span class="n">h</span> <span class="o">|</span> <span class="n">o</span> <span class="o">|</span> <span class="n">n</span> <span class="o">|</span>
<span class="o">+---+---+---+---+---+---+</span>
<span class="mi">0</span> <span class="mi">1</span> <span class="mi">2</span> <span class="mi">3</span> <span class="mi">4</span> <span class="mi">5</span> <span class="mi">6</span>
<span class="o">-</span><span class="mi">6</span> <span class="o">-</span><span class="mi">5</span> <span class="o">-</span><span class="mi">4</span> <span class="o">-</span><span class="mi">3</span> <span class="o">-</span><span class="mi">2</span> <span class="o">-</span><span class="mi">1</span>
</pre></div>
<p>第一行数字给出字符串正索引点值0...5 。第二行给出相应的负索引。切片是从 i 到 j 两个数值标示的边界之间的所有字符。</p>
<p>对于非负索引，如果两个索引都在边界内，切片长度就是两个索引之差。例如， word[1:3] 是 2 。</p>
<p>切片时，下标溢出不会报错。</p>
<div class="highlight"><pre><span></span>>>> word[4:42]
'on'
>>> word[43:42]
''
</pre></div>
<p>Python的字符串是不可变。向字符串文本的某一个索引赋值会引发错误:</p>
<div class="highlight"><pre><span></span>>>> word[0] = 'J'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: 'str' object does not support item assignment
</pre></div>
<p>通过联合(加号)可以简单高效的创建字符串。（注，jython中这种操作并不高效）。</p>
<div class="highlight"><pre><span></span>>>> 'J' + word[1:]
'Jython'
>>> word[:2] + 'py'
'Pypy'
</pre></div>
<p>内置函数len()返回字符串长度:</p>
<div class="highlight"><pre><span></span>>>> s = 'supercalifragilisticexpialidocious'
>>> len(s)
34
</pre></div>
<ul>
<li>试题</li>
</ul>
<p>1，下面哪个个字符串定义有错误？</p>
<p>A，r'C:\Program Files\foo\bar'
B，r'C:\Program Files\foo\bar\'
C, r'C:\Program Files\foo\bar\'
D，r'C:\Program Files\foo\bar\\'</p>
<p>2，min('abcd')的结果是？</p>
<p>A，a B，b |C，c D，d</p>
<p>2，max('abcd3A')的结果是？
A，a B，3 |C，A D，d</p>
<h2 id="_2">参考资料</h2>
<ul>
<li>Sequence Types — str, unicode, list, tuple, bytearray, buffer, xrange <a href="https://docs.python.org/3/tutorial/introduction.html#strings">https://docs.python.org/3/tutorial/introduction.html#strings</a> </li>
<li>String Methods: <a href="https://docs.python.org/3/library/stdtypes.html#string-methods">https://docs.python.org/3/library/stdtypes.html#string-methods</a></li>
<li>String Formatting：<a href="https://docs.python.org/3/library/string.html#new-string-formatting">https://docs.python.org/3/library/string.html#new-string-formatting</a></li>
<li>String Formatting Operations: <a href="https://docs.python.org/2/library/stdtypes.html#string-formatting">https://docs.python.org/2/library/stdtypes.html#string-formatting</a></li>
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<li><a href="https://china-testing.github.io/python3_crash6.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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