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<h1 id="">字节对编码标记化</h1>


<div class="flex space-x-1 absolute z-10 right-0 top-0"><a href="https://discuss.huggingface.co/t/chapter-6-questions" target="_blank"><img alt="Ask a Question" class="!m-0" src="https://img.shields.io/badge/Ask%20a%20question-ffcb4c.svg?logo=data:image/svg+xml;base64,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"></a>
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<p>字节对编码(BPE)最初被开发为一种压缩文本的算法,然后在预训练 GPT 模型时被 OpenAI 用于标记化。许多 Transformer 模型都使用它,包括 GPT、GPT-2、RoBERTa、BART 和 DeBERTa。</p>
<iframe class="w-full xl:w-4/6 h-80" src="https://www.youtube-nocookie.com/embed/HEikzVL-lZU" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>


<div class="course-tip  bg-gradient-to-br dark:bg-gradient-to-r before:border-green-500 dark:before:border-green-800 from-green-50 dark:from-gray-900 to-white dark:to-gray-950 border border-green-50 text-green-700 dark:text-gray-400"><p>💡 本节深入介绍了BPE,甚至展示了一个完整的实现。如果你只想大致了解标记化算法,可以跳到最后。</p></div>
<h2 id="">训练算法</h2>
<p>BPE 训练首先计算语料库中使用的唯一单词集(在完成标准化和预标记化步骤之后),然后通过获取用于编写这些单词的所有符号来构建词汇表。一个非常简单的例子,假设我们的语料库使用了这五个词:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
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	<pre><!-- HTML_TAG_START --><span class="hljs-string">&quot;hug&quot;</span>, <span class="hljs-string">&quot;pug&quot;</span>, <span class="hljs-string">&quot;pun&quot;</span>, <span class="hljs-string">&quot;bun&quot;</span>, <span class="hljs-string">&quot;hugs&quot;</span><!-- HTML_TAG_END --></pre></div>
<p>基础词汇将是 <code>[&quot;b&quot;, &quot;g&quot;, &quot;h&quot;, &quot;n&quot;, &quot;p&quot;, &quot;s&quot;, &quot;u&quot;]</code>。对于实际情况,基本词汇表将包含所有 ASCII 字符,至少,可能还包含一些 Unicode 字符。如果您正在标记的示例使用不在训练语料库中的字符,则该字符将转换为未知标记。这就是为什么许多 NLP 模型在分析带有表情符号的内容方面非常糟糕的原因之一。</p>


<div class="course-tip  bg-gradient-to-br dark:bg-gradient-to-r before:border-green-500 dark:before:border-green-800 from-green-50 dark:from-gray-900 to-white dark:to-gray-950 border border-green-50 text-green-700 dark:text-gray-400"><p>TGPT-2 和 RoBERTa 标记器(非常相似)有一个聪明的方法来处理这个问题: 他们不把单词看成是用 Unicode 字符写的，而是用字节写的。这样,基本词汇表的大小很小(256),但你能想到的每个字符仍将被包含在内,而不会最终转换为未知标记。这个技巧被称为 <em>字节级 BPE</em>。</p></div>
<p>获得这个基本词汇后,我们添加新的标记,直到通过学习<em>合并</em>达到所需的词汇量,这是将现有词汇表的两个元素合并为一个新元素的规则。因此,在开始时,这些合并将创建具有两个字符的标记,然后,随着训练的进行,会创建更长的子词。</p>
<p>在分词器训练期间的任何一步,BPE 算法都会搜索最常见的现有标记对 (“对”,这里我们指的是单词中的两个连续标记)。最频繁的一对将被合并,我们冲洗并重复下一步。</p>
<p>回到我们之前的例子,让我们假设单词具有以下频率:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
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	<pre><!-- HTML_TAG_START -->(<span class="hljs-string">&quot;hug&quot;</span><span class="hljs-punctuation">,</span> <span class="hljs-number">10</span>)<span class="hljs-punctuation">,</span> (<span class="hljs-string">&quot;pug&quot;</span><span class="hljs-punctuation">,</span> <span class="hljs-number">5</span>)<span class="hljs-punctuation">,</span> (<span class="hljs-string">&quot;pun&quot;</span><span class="hljs-punctuation">,</span> <span class="hljs-number">12</span>)<span class="hljs-punctuation">,</span> (<span class="hljs-string">&quot;bun&quot;</span><span class="hljs-punctuation">,</span> <span class="hljs-number">4</span>)<span class="hljs-punctuation">,</span> (<span class="hljs-string">&quot;hugs&quot;</span><span class="hljs-punctuation">,</span> <span class="hljs-number">5</span>)<!-- HTML_TAG_END --></pre></div>
<p>意味着 <code>&quot;hug&quot;</code> 在语料库中出现了10次, <code>&quot;pug&quot;</code> 5次, <code>&quot;pun&quot;</code> 12次, <code>&quot;bun&quot;</code> 4次, 以及 <code>&quot;hugs&quot;</code> 5次。我们通过将每个单词拆分为字符(形成我们初始词汇表的字符)来开始训练,这样我们就可以将每个单词视为一个标记列表:</p>

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	<pre><!-- HTML_TAG_START -->(<span class="hljs-string">&quot;h&quot;</span> <span class="hljs-string">&quot;u&quot;</span> <span class="hljs-string">&quot;g&quot;</span><span class="hljs-punctuation">,</span> <span class="hljs-number">10</span>)<span class="hljs-punctuation">,</span> (<span class="hljs-string">&quot;p&quot;</span> <span class="hljs-string">&quot;u&quot;</span> <span class="hljs-string">&quot;g&quot;</span><span class="hljs-punctuation">,</span> <span class="hljs-number">5</span>)<span class="hljs-punctuation">,</span> (<span class="hljs-string">&quot;p&quot;</span> <span class="hljs-string">&quot;u&quot;</span> <span class="hljs-string">&quot;n&quot;</span><span class="hljs-punctuation">,</span> <span class="hljs-number">12</span>)<span class="hljs-punctuation">,</span> (<span class="hljs-string">&quot;b&quot;</span> <span class="hljs-string">&quot;u&quot;</span> <span class="hljs-string">&quot;n&quot;</span><span class="hljs-punctuation">,</span> <span class="hljs-number">4</span>)<span class="hljs-punctuation">,</span> (<span class="hljs-string">&quot;h&quot;</span> <span class="hljs-string">&quot;u&quot;</span> <span class="hljs-string">&quot;g&quot;</span> <span class="hljs-string">&quot;s&quot;</span><span class="hljs-punctuation">,</span> <span class="hljs-number">5</span>)<!-- HTML_TAG_END --></pre></div>
<p>然后我们看成对。这对 <code>(&quot;h&quot;, &quot;u&quot;)</code> 出现在单词 <code>&quot;hug&quot;</code> 和 <code>&quot;hugs&quot;</code>中,所以语料库中总共有15次。不过,这并不是最频繁的一对:这个荣誉属于 <code>(&quot;u&quot;, &quot;g&quot;)</code>,它出现在 <code>&quot;hug&quot;</code>, <code>&quot;pug&quot;</code>, 以及 <code>&quot;hugs&quot;</code>中,在词汇表中总共 20 次。</p>
<p>因此,标记器学习的第一个合并规则是 <code>(&quot;u&quot;, &quot;g&quot;) -&gt; &quot;ug&quot;</code>,意思就是 <code>&quot;ug&quot;</code> 将被添加到词汇表中,并且这对应该合并到语料库的所有单词中。在这个阶段结束时,词汇表和语料库看起来像这样:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
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	<pre><!-- HTML_TAG_START --><span class="hljs-symbol">Vocabulary:</span> [<span class="hljs-string">&quot;b&quot;</span>, <span class="hljs-string">&quot;g&quot;</span>, <span class="hljs-string">&quot;h&quot;</span>, <span class="hljs-string">&quot;n&quot;</span>, <span class="hljs-string">&quot;p&quot;</span>, <span class="hljs-string">&quot;s&quot;</span>, <span class="hljs-string">&quot;u&quot;</span>, <span class="hljs-string">&quot;ug&quot;</span>]
<span class="hljs-symbol">Corpus:</span> (<span class="hljs-string">&quot;h&quot;</span> <span class="hljs-string">&quot;ug&quot;</span>, <span class="hljs-number">10</span>), (<span class="hljs-string">&quot;p&quot;</span> <span class="hljs-string">&quot;ug&quot;</span>, <span class="hljs-number">5</span>), (<span class="hljs-string">&quot;p&quot;</span> <span class="hljs-string">&quot;u&quot;</span> <span class="hljs-string">&quot;n&quot;</span>, <span class="hljs-number">12</span>), (<span class="hljs-string">&quot;b&quot;</span> <span class="hljs-string">&quot;u&quot;</span> <span class="hljs-string">&quot;n&quot;</span>, <span class="hljs-number">4</span>), (<span class="hljs-string">&quot;h&quot;</span> <span class="hljs-string">&quot;ug&quot;</span> <span class="hljs-string">&quot;s&quot;</span>, <span class="hljs-number">5</span>)<!-- HTML_TAG_END --></pre></div>
<p>现在我们有一些导致标记长于两个字符的对: 例如 <code>(&quot;h&quot;, &quot;ug&quot;)</code>, 在语料库中出现15次。然而,这个阶段最频繁的对是 <code>(&quot;u&quot;, &quot;n&quot;)</code>,在语料库中出现16次,所以学到的第二个合并规则是 <code>(&quot;u&quot;, &quot;n&quot;) -&gt; &quot;un&quot;</code>。将其添加到词汇表并合并所有现有的这个对,将出现:</p>

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	<pre><!-- HTML_TAG_START --><span class="hljs-symbol">Vocabulary:</span> [<span class="hljs-string">&quot;b&quot;</span>, <span class="hljs-string">&quot;g&quot;</span>, <span class="hljs-string">&quot;h&quot;</span>, <span class="hljs-string">&quot;n&quot;</span>, <span class="hljs-string">&quot;p&quot;</span>, <span class="hljs-string">&quot;s&quot;</span>, <span class="hljs-string">&quot;u&quot;</span>, <span class="hljs-string">&quot;ug&quot;</span>, <span class="hljs-string">&quot;un&quot;</span>]
<span class="hljs-symbol">Corpus:</span> (<span class="hljs-string">&quot;h&quot;</span> <span class="hljs-string">&quot;ug&quot;</span>, <span class="hljs-number">10</span>), (<span class="hljs-string">&quot;p&quot;</span> <span class="hljs-string">&quot;ug&quot;</span>, <span class="hljs-number">5</span>), (<span class="hljs-string">&quot;p&quot;</span> <span class="hljs-string">&quot;un&quot;</span>, <span class="hljs-number">12</span>), (<span class="hljs-string">&quot;b&quot;</span> <span class="hljs-string">&quot;un&quot;</span>, <span class="hljs-number">4</span>), (<span class="hljs-string">&quot;h&quot;</span> <span class="hljs-string">&quot;ug&quot;</span> <span class="hljs-string">&quot;s&quot;</span>, <span class="hljs-number">5</span>)<!-- HTML_TAG_END --></pre></div>
<p>现在最频繁的一对是 <code>(&quot;h&quot;, &quot;ug&quot;)</code>,所以我们学习了合并规则 <code>(&quot;h&quot;, &quot;ug&quot;) -&gt; &quot;hug&quot;</code>,这给了我们第一个三个字母的标记。合并后,语料库如下所示:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START --><span class="hljs-symbol">Vocabulary:</span> [<span class="hljs-string">&quot;b&quot;</span>, <span class="hljs-string">&quot;g&quot;</span>, <span class="hljs-string">&quot;h&quot;</span>, <span class="hljs-string">&quot;n&quot;</span>, <span class="hljs-string">&quot;p&quot;</span>, <span class="hljs-string">&quot;s&quot;</span>, <span class="hljs-string">&quot;u&quot;</span>, <span class="hljs-string">&quot;ug&quot;</span>, <span class="hljs-string">&quot;un&quot;</span>, <span class="hljs-string">&quot;hug&quot;</span>]
<span class="hljs-symbol">Corpus:</span> (<span class="hljs-string">&quot;hug&quot;</span>, <span class="hljs-number">10</span>), (<span class="hljs-string">&quot;p&quot;</span> <span class="hljs-string">&quot;ug&quot;</span>, <span class="hljs-number">5</span>), (<span class="hljs-string">&quot;p&quot;</span> <span class="hljs-string">&quot;un&quot;</span>, <span class="hljs-number">12</span>), (<span class="hljs-string">&quot;b&quot;</span> <span class="hljs-string">&quot;un&quot;</span>, <span class="hljs-number">4</span>), (<span class="hljs-string">&quot;hug&quot;</span> <span class="hljs-string">&quot;s&quot;</span>, <span class="hljs-number">5</span>)<!-- HTML_TAG_END --></pre></div>
<p>我们继续这样合并,直到达到我们所需的词汇量。</p>


<div class="course-tip  bg-gradient-to-br dark:bg-gradient-to-r before:border-green-500 dark:before:border-green-800 from-green-50 dark:from-gray-900 to-white dark:to-gray-950 border border-green-50 text-green-700 dark:text-gray-400"><p>✏️ <strong>现在轮到你了!</strong>你认为下一个合并规则是什么？</p></div>
<h2 id="">标记化算法</h2>
<p>标记化紧跟训练过程,从某种意义上说,通过应用以下步骤对新输入进行标记:</p>
<ol><li>规范化</li>
<li>预标记化</li>
<li>将单词拆分为单个字符</li>
<li>将学习的合并规则按顺序应用于这些拆分</li></ol>
<p>让我们以我们在训练期间使用的示例为例,学习三个合并规则:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START --><span class="hljs-function"><span class="hljs-params">(<span class="hljs-string">&quot;u&quot;</span>, <span class="hljs-string">&quot;g&quot;</span>)</span> -&gt;</span> <span class="hljs-string">&quot;ug&quot;</span>
<span class="hljs-function"><span class="hljs-params">(<span class="hljs-string">&quot;u&quot;</span>, <span class="hljs-string">&quot;n&quot;</span>)</span> -&gt;</span> <span class="hljs-string">&quot;un&quot;</span>
<span class="hljs-function"><span class="hljs-params">(<span class="hljs-string">&quot;h&quot;</span>, <span class="hljs-string">&quot;ug&quot;</span>)</span> -&gt;</span> <span class="hljs-string">&quot;hug&quot;</span><!-- HTML_TAG_END --></pre></div>
<p>这个单词 <code>&quot;bug&quot;</code> 将被标记为 <code>[&quot;b&quot;, &quot;ug&quot;]</code>。然而 <code>&quot;mug&quot;</code>,将被标记为 <code>[&quot;[UNK]&quot;, &quot;ug&quot;]</code>,因为字母 <code>&quot;m&quot;</code> 不再基本词汇表中。同样,单词<code>&quot;thug&quot;</code> 会被标记为 <code>[&quot;[UNK]&quot;, &quot;hug&quot;]</code>: 字母 <code>&quot;t&quot;</code> 不在基本词汇表中,应用合并规则首先导致 <code>&quot;u&quot;</code> 和 <code>&quot;g&quot;</code> 被合并,然后是 <code>&quot;hu&quot;</code> 和 <code>&quot;g&quot;</code> 被合并。</p>


<div class="course-tip  bg-gradient-to-br dark:bg-gradient-to-r before:border-green-500 dark:before:border-green-800 from-green-50 dark:from-gray-900 to-white dark:to-gray-950 border border-green-50 text-green-700 dark:text-gray-400"><p>✏️ <strong>现在轮到你了!</strong> 你认为这个词 <code>&quot;unhug&quot;</code> 将如何被标记？</p></div>
<h2 class="relative group"><a id="bpe" class="header-link block pr-1.5 text-lg no-hover:hidden with-hover:absolute with-hover:p-1.5 with-hover:opacity-0 with-hover:group-hover:opacity-100 with-hover:right-full" href="#bpe"><span><svg class="" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" aria-hidden="true" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 256 256"><path d="M167.594 88.393a8.001 8.001 0 0 1 0 11.314l-67.882 67.882a8 8 0 1 1-11.314-11.315l67.882-67.881a8.003 8.003 0 0 1 11.314 0zm-28.287 84.86l-28.284 28.284a40 40 0 0 1-56.567-56.567l28.284-28.284a8 8 0 0 0-11.315-11.315l-28.284 28.284a56 56 0 0 0 79.196 79.197l28.285-28.285a8 8 0 1 0-11.315-11.314zM212.852 43.14a56.002 56.002 0 0 0-79.196 0l-28.284 28.284a8 8 0 1 0 11.314 11.314l28.284-28.284a40 40 0 0 1 56.568 56.567l-28.285 28.285a8 8 0 0 0 11.315 11.314l28.284-28.284a56.065 56.065 0 0 0 0-79.196z" fill="currentColor"></path></svg></span></a>
	<span>实现 BPE
	</span></h2>

<p>现在让我们看一下 BPE 算法的实现。这不会是你可以在大型语料库上实际使用的优化版本;我们只是想向你展示代码,以便你可以更好地理解算法</p>
<p>首先我们需要一个语料库,所以让我们用几句话创建一个简单的语料库:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
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	<pre><!-- HTML_TAG_START -->corpus = [
    <span class="hljs-string">&quot;This is the Hugging Face course.&quot;</span>,
    <span class="hljs-string">&quot;This chapter is about tokenization.&quot;</span>,
    <span class="hljs-string">&quot;This section shows several tokenizer algorithms.&quot;</span>,
    <span class="hljs-string">&quot;Hopefully, you will be able to understand how they are trained and generate tokens.&quot;</span>,
]<!-- HTML_TAG_END --></pre></div>
<p>接下来,我们需要将该语料库预先标记为单词。由于我们正在复制 BPE 标记器(如 GPT-2),我们将使用 <code>gpt2</code> 标记器作为预标记化的标记器:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START --><span class="hljs-keyword">from</span> transformers <span class="hljs-keyword">import</span> AutoTokenizer

tokenizer = AutoTokenizer.from_pretrained(<span class="hljs-string">&quot;gpt2&quot;</span>)<!-- HTML_TAG_END --></pre></div>
<p>然后我们在进行预标记化时计算语料库中每个单词的频率:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START --><span class="hljs-keyword">from</span> collections <span class="hljs-keyword">import</span> defaultdict

word_freqs = defaultdict(<span class="hljs-built_in">int</span>)

<span class="hljs-keyword">for</span> text <span class="hljs-keyword">in</span> corpus:
    words_with_offsets = tokenizer.backend_tokenizer.pre_tokenizer.pre_tokenize_str(text)
    new_words = [word <span class="hljs-keyword">for</span> word, offset <span class="hljs-keyword">in</span> words_with_offsets]
    <span class="hljs-keyword">for</span> word <span class="hljs-keyword">in</span> new_words:
        word_freqs[word] += <span class="hljs-number">1</span>

<span class="hljs-built_in">print</span>(word_freqs)<!-- HTML_TAG_END --></pre></div>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START -->defaultdict(<span class="hljs-built_in">int</span>, {<span class="hljs-string">&#x27;This&#x27;</span>: <span class="hljs-number">3</span>, <span class="hljs-string">&#x27;Ġis&#x27;</span>: <span class="hljs-number">2</span>, <span class="hljs-string">&#x27;Ġthe&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;ĠHugging&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;ĠFace&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;ĠCourse&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;.&#x27;</span>: <span class="hljs-number">4</span>, <span class="hljs-string">&#x27;Ġchapter&#x27;</span>: <span class="hljs-number">1</span>,
    <span class="hljs-string">&#x27;Ġabout&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġtokenization&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġsection&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġshows&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġseveral&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġtokenizer&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġalgorithms&#x27;</span>: <span class="hljs-number">1</span>,
    <span class="hljs-string">&#x27;Hopefully&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;,&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġyou&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġwill&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġbe&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġable&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġto&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġunderstand&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġhow&#x27;</span>: <span class="hljs-number">1</span>,
    <span class="hljs-string">&#x27;Ġthey&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġare&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġtrained&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġand&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġgenerate&#x27;</span>: <span class="hljs-number">1</span>, <span class="hljs-string">&#x27;Ġtokens&#x27;</span>: <span class="hljs-number">1</span>})<!-- HTML_TAG_END --></pre></div>
<p>下一步是计算基本词汇,由语料库中使用的所有字符组成:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START -->alphabet = []

<span class="hljs-keyword">for</span> word <span class="hljs-keyword">in</span> word_freqs.keys():
    <span class="hljs-keyword">for</span> letter <span class="hljs-keyword">in</span> word:
        <span class="hljs-keyword">if</span> letter <span class="hljs-keyword">not</span> <span class="hljs-keyword">in</span> alphabet:
            alphabet.append(letter)
alphabet.sort()

<span class="hljs-built_in">print</span>(alphabet)<!-- HTML_TAG_END --></pre></div>

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	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START -->[ <span class="hljs-string">&#x27;,&#x27;</span>, <span class="hljs-string">&#x27;.&#x27;</span>, <span class="hljs-string">&#x27;C&#x27;</span>, <span class="hljs-string">&#x27;F&#x27;</span>, <span class="hljs-string">&#x27;H&#x27;</span>, <span class="hljs-string">&#x27;T&#x27;</span>, <span class="hljs-string">&#x27;a&#x27;</span>, <span class="hljs-string">&#x27;b&#x27;</span>, <span class="hljs-string">&#x27;c&#x27;</span>, <span class="hljs-string">&#x27;d&#x27;</span>, <span class="hljs-string">&#x27;e&#x27;</span>, <span class="hljs-string">&#x27;f&#x27;</span>, <span class="hljs-string">&#x27;g&#x27;</span>, <span class="hljs-string">&#x27;h&#x27;</span>, <span class="hljs-string">&#x27;i&#x27;</span>, <span class="hljs-string">&#x27;k&#x27;</span>, <span class="hljs-string">&#x27;l&#x27;</span>, <span class="hljs-string">&#x27;m&#x27;</span>, <span class="hljs-string">&#x27;n&#x27;</span>, <span class="hljs-string">&#x27;o&#x27;</span>, <span class="hljs-string">&#x27;p&#x27;</span>, <span class="hljs-string">&#x27;r&#x27;</span>, <span class="hljs-string">&#x27;s&#x27;</span>,
  <span class="hljs-string">&#x27;t&#x27;</span>, <span class="hljs-string">&#x27;u&#x27;</span>, <span class="hljs-string">&#x27;v&#x27;</span>, <span class="hljs-string">&#x27;w&#x27;</span>, <span class="hljs-string">&#x27;y&#x27;</span>, <span class="hljs-string">&#x27;z&#x27;</span>, <span class="hljs-string">&#x27;Ġ&#x27;</span>]<!-- HTML_TAG_END --></pre></div>
<p>我们还在该词汇表的开头添加了模型使用的特殊标记。对于GPT-2,唯一的特殊标记是 <code>&quot;&lt;|endoftext|&gt;&quot;</code>:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START -->vocab = [<span class="hljs-string">&quot;&lt;|endoftext|&gt;&quot;</span>] + alphabet.copy()<!-- HTML_TAG_END --></pre></div>
<p>我们现在需要将每个单词拆分为单独的字符,以便能够开始训练:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START -->splits = {word: [c <span class="hljs-keyword">for</span> c <span class="hljs-keyword">in</span> word] <span class="hljs-keyword">for</span> word <span class="hljs-keyword">in</span> word_freqs.keys()}<!-- HTML_TAG_END --></pre></div>
<p>现在我们已准备好进行训练,让我们编写一个函数来计算每对的频率。我们需要在训练的每个步骤中使用它:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START --><span class="hljs-keyword">def</span> <span class="hljs-title function_">compute_pair_freqs</span>(<span class="hljs-params">splits</span>):
    pair_freqs = defaultdict(<span class="hljs-built_in">int</span>)
    <span class="hljs-keyword">for</span> word, freq <span class="hljs-keyword">in</span> word_freqs.items():
        split = splits[word]
        <span class="hljs-keyword">if</span> <span class="hljs-built_in">len</span>(split) == <span class="hljs-number">1</span>:
            <span class="hljs-keyword">continue</span>
        <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-built_in">range</span>(<span class="hljs-built_in">len</span>(split) - <span class="hljs-number">1</span>):
            pair = (split[i], split[i + <span class="hljs-number">1</span>])
            pair_freqs[pair] += freq
    <span class="hljs-keyword">return</span> pair_freqs<!-- HTML_TAG_END --></pre></div>
<p>让我们来看看这个字典在初始拆分后的一部分:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START -->pair_freqs = compute_pair_freqs(splits)

<span class="hljs-keyword">for</span> i, key <span class="hljs-keyword">in</span> <span class="hljs-built_in">enumerate</span>(pair_freqs.keys()):
    <span class="hljs-built_in">print</span>(<span class="hljs-string">f&quot;<span class="hljs-subst">{key}</span>: <span class="hljs-subst">{pair_freqs[key]}</span>&quot;</span>)
    <span class="hljs-keyword">if</span> i &gt;= <span class="hljs-number">5</span>:
        <span class="hljs-keyword">break</span><!-- HTML_TAG_END --></pre></div>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START -->(<span class="hljs-string">&#x27;T&#x27;</span>, <span class="hljs-string">&#x27;h&#x27;</span>): <span class="hljs-number">3</span>
(<span class="hljs-string">&#x27;h&#x27;</span>, <span class="hljs-string">&#x27;i&#x27;</span>): <span class="hljs-number">3</span>
(<span class="hljs-string">&#x27;i&#x27;</span>, <span class="hljs-string">&#x27;s&#x27;</span>): <span class="hljs-number">5</span>
(<span class="hljs-string">&#x27;Ġ&#x27;</span>, <span class="hljs-string">&#x27;i&#x27;</span>): <span class="hljs-number">2</span>
(<span class="hljs-string">&#x27;Ġ&#x27;</span>, <span class="hljs-string">&#x27;t&#x27;</span>): <span class="hljs-number">7</span>
(<span class="hljs-string">&#x27;t&#x27;</span>, <span class="hljs-string">&#x27;h&#x27;</span>): <span class="hljs-number">3</span><!-- HTML_TAG_END --></pre></div>
<p>现在, 找到最频繁的对只需要一个快速的循环:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START -->best_pair = <span class="hljs-string">&quot;&quot;</span>
max_freq = <span class="hljs-literal">None</span>

<span class="hljs-keyword">for</span> pair, freq <span class="hljs-keyword">in</span> pair_freqs.items():
    <span class="hljs-keyword">if</span> max_freq <span class="hljs-keyword">is</span> <span class="hljs-literal">None</span> <span class="hljs-keyword">or</span> max_freq &lt; freq:
        best_pair = pair
        max_freq = freq

<span class="hljs-built_in">print</span>(best_pair, max_freq)<!-- HTML_TAG_END --></pre></div>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START -->(<span class="hljs-string">&#x27;Ġ&#x27;</span>, <span class="hljs-string">&#x27;t&#x27;</span>) <span class="hljs-number">7</span><!-- HTML_TAG_END --></pre></div>
<p>所以第一个要学习的合并是 <code>(&#39;Ġ&#39;, &#39;t&#39;) -&gt; &#39;Ġt&#39;</code>, 我们添加 <code>&#39;Ġt&#39;</code> 到词汇表:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START -->merges = {(<span class="hljs-string">&quot;Ġ&quot;</span>, <span class="hljs-string">&quot;t&quot;</span>): <span class="hljs-string">&quot;Ġt&quot;</span>}
vocab.append(<span class="hljs-string">&quot;Ġt&quot;</span>)<!-- HTML_TAG_END --></pre></div>
<p>要继续接下来的步骤,我们需要在我们的<code>分词</code>字典中应用该合并。让我们为此编写另一个函数:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START --><span class="hljs-keyword">def</span> <span class="hljs-title function_">merge_pair</span>(<span class="hljs-params">a, b, splits</span>):
    <span class="hljs-keyword">for</span> word <span class="hljs-keyword">in</span> word_freqs:
        split = splits[word]
        <span class="hljs-keyword">if</span> <span class="hljs-built_in">len</span>(split) == <span class="hljs-number">1</span>:
            <span class="hljs-keyword">continue</span>

        i = <span class="hljs-number">0</span>
        <span class="hljs-keyword">while</span> i &lt; <span class="hljs-built_in">len</span>(split) - <span class="hljs-number">1</span>:
            <span class="hljs-keyword">if</span> split[i] == a <span class="hljs-keyword">and</span> split[i + <span class="hljs-number">1</span>] == b:
                split = split[:i] + [a + b] + split[i + <span class="hljs-number">2</span> :]
            <span class="hljs-keyword">else</span>:
                i += <span class="hljs-number">1</span>
        splits[word] = split
    <span class="hljs-keyword">return</span> splits<!-- HTML_TAG_END --></pre></div>
<p>我们可以看看第一次合并的结果:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START -->splits = merge_pair(<span class="hljs-string">&quot;Ġ&quot;</span>, <span class="hljs-string">&quot;t&quot;</span>, splits)
<span class="hljs-built_in">print</span>(splits[<span class="hljs-string">&quot;Ġtrained&quot;</span>])<!-- HTML_TAG_END --></pre></div>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
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	<pre><!-- HTML_TAG_START -->[<span class="hljs-string">&#x27;Ġt&#x27;</span>, <span class="hljs-string">&#x27;r&#x27;</span>, <span class="hljs-string">&#x27;a&#x27;</span>, <span class="hljs-string">&#x27;i&#x27;</span>, <span class="hljs-string">&#x27;n&#x27;</span>, <span class="hljs-string">&#x27;e&#x27;</span>, <span class="hljs-string">&#x27;d&#x27;</span>]<!-- HTML_TAG_END --></pre></div>
<p>现在我们有了循环所需的一切,直到我们学会了我们想要的所有合并。我们的目标是词汇量达到50:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
	Copied</div></button></div>
	<pre><!-- HTML_TAG_START -->vocab_size = <span class="hljs-number">50</span>

<span class="hljs-keyword">while</span> <span class="hljs-built_in">len</span>(vocab) &lt; vocab_size:
    pair_freqs = compute_pair_freqs(splits)
    best_pair = <span class="hljs-string">&quot;&quot;</span>
    max_freq = <span class="hljs-literal">None</span>
    <span class="hljs-keyword">for</span> pair, freq <span class="hljs-keyword">in</span> pair_freqs.items():
        <span class="hljs-keyword">if</span> max_freq <span class="hljs-keyword">is</span> <span class="hljs-literal">None</span> <span class="hljs-keyword">or</span> max_freq &lt; freq:
            best_pair = pair
            max_freq = freq
    splits = merge_pair(*best_pair, splits)
    merges[best_pair] = best_pair[<span class="hljs-number">0</span>] + best_pair[<span class="hljs-number">1</span>]
    vocab.append(best_pair[<span class="hljs-number">0</span>] + best_pair[<span class="hljs-number">1</span>])<!-- HTML_TAG_END --></pre></div>
<p>结果,我们学习了 19 条合并规则(初始词汇表的大小 31 — 30 字母字符,加上特殊标记):</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
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	Copied</div></button></div>
	<pre><!-- HTML_TAG_START --><span class="hljs-built_in">print</span>(merges)<!-- HTML_TAG_END --></pre></div>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
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	Copied</div></button></div>
	<pre><!-- HTML_TAG_START -->{(<span class="hljs-string">&#x27;Ġ&#x27;</span>, <span class="hljs-string">&#x27;t&#x27;</span>): <span class="hljs-string">&#x27;Ġt&#x27;</span>, (<span class="hljs-string">&#x27;i&#x27;</span>, <span class="hljs-string">&#x27;s&#x27;</span>): <span class="hljs-string">&#x27;is&#x27;</span>, (<span class="hljs-string">&#x27;e&#x27;</span>, <span class="hljs-string">&#x27;r&#x27;</span>): <span class="hljs-string">&#x27;er&#x27;</span>, (<span class="hljs-string">&#x27;Ġ&#x27;</span>, <span class="hljs-string">&#x27;a&#x27;</span>): <span class="hljs-string">&#x27;Ġa&#x27;</span>, (<span class="hljs-string">&#x27;Ġt&#x27;</span>, <span class="hljs-string">&#x27;o&#x27;</span>): <span class="hljs-string">&#x27;Ġto&#x27;</span>, (<span class="hljs-string">&#x27;e&#x27;</span>, <span class="hljs-string">&#x27;n&#x27;</span>): <span class="hljs-string">&#x27;en&#x27;</span>,
 (<span class="hljs-string">&#x27;T&#x27;</span>, <span class="hljs-string">&#x27;h&#x27;</span>): <span class="hljs-string">&#x27;Th&#x27;</span>, (<span class="hljs-string">&#x27;Th&#x27;</span>, <span class="hljs-string">&#x27;is&#x27;</span>): <span class="hljs-string">&#x27;This&#x27;</span>, (<span class="hljs-string">&#x27;o&#x27;</span>, <span class="hljs-string">&#x27;u&#x27;</span>): <span class="hljs-string">&#x27;ou&#x27;</span>, (<span class="hljs-string">&#x27;s&#x27;</span>, <span class="hljs-string">&#x27;e&#x27;</span>): <span class="hljs-string">&#x27;se&#x27;</span>, (<span class="hljs-string">&#x27;Ġto&#x27;</span>, <span class="hljs-string">&#x27;k&#x27;</span>): <span class="hljs-string">&#x27;Ġtok&#x27;</span>,
 (<span class="hljs-string">&#x27;Ġtok&#x27;</span>, <span class="hljs-string">&#x27;en&#x27;</span>): <span class="hljs-string">&#x27;Ġtoken&#x27;</span>, (<span class="hljs-string">&#x27;n&#x27;</span>, <span class="hljs-string">&#x27;d&#x27;</span>): <span class="hljs-string">&#x27;nd&#x27;</span>, (<span class="hljs-string">&#x27;Ġ&#x27;</span>, <span class="hljs-string">&#x27;is&#x27;</span>): <span class="hljs-string">&#x27;Ġis&#x27;</span>, (<span class="hljs-string">&#x27;Ġt&#x27;</span>, <span class="hljs-string">&#x27;h&#x27;</span>): <span class="hljs-string">&#x27;Ġth&#x27;</span>, (<span class="hljs-string">&#x27;Ġth&#x27;</span>, <span class="hljs-string">&#x27;e&#x27;</span>): <span class="hljs-string">&#x27;Ġthe&#x27;</span>,
 (<span class="hljs-string">&#x27;i&#x27;</span>, <span class="hljs-string">&#x27;n&#x27;</span>): <span class="hljs-string">&#x27;in&#x27;</span>, (<span class="hljs-string">&#x27;Ġa&#x27;</span>, <span class="hljs-string">&#x27;b&#x27;</span>): <span class="hljs-string">&#x27;Ġab&#x27;</span>, (<span class="hljs-string">&#x27;Ġtoken&#x27;</span>, <span class="hljs-string">&#x27;i&#x27;</span>): <span class="hljs-string">&#x27;Ġtokeni&#x27;</span>}<!-- HTML_TAG_END --></pre></div>
<p>词汇表由特殊标记、初始字母和所有合并结果组成:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
	Copied</div></button></div>
	<pre><!-- HTML_TAG_START --><span class="hljs-built_in">print</span>(vocab)<!-- HTML_TAG_END --></pre></div>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
	Copied</div></button></div>
	<pre><!-- HTML_TAG_START -->[<span class="hljs-string">&#x27;&lt;|endoftext|&gt;&#x27;</span>, <span class="hljs-string">&#x27;,&#x27;</span>, <span class="hljs-string">&#x27;.&#x27;</span>, <span class="hljs-string">&#x27;C&#x27;</span>, <span class="hljs-string">&#x27;F&#x27;</span>, <span class="hljs-string">&#x27;H&#x27;</span>, <span class="hljs-string">&#x27;T&#x27;</span>, <span class="hljs-string">&#x27;a&#x27;</span>, <span class="hljs-string">&#x27;b&#x27;</span>, <span class="hljs-string">&#x27;c&#x27;</span>, <span class="hljs-string">&#x27;d&#x27;</span>, <span class="hljs-string">&#x27;e&#x27;</span>, <span class="hljs-string">&#x27;f&#x27;</span>, <span class="hljs-string">&#x27;g&#x27;</span>, <span class="hljs-string">&#x27;h&#x27;</span>, <span class="hljs-string">&#x27;i&#x27;</span>, <span class="hljs-string">&#x27;k&#x27;</span>, <span class="hljs-string">&#x27;l&#x27;</span>, <span class="hljs-string">&#x27;m&#x27;</span>, <span class="hljs-string">&#x27;n&#x27;</span>, <span class="hljs-string">&#x27;o&#x27;</span>,
 <span class="hljs-string">&#x27;p&#x27;</span>, <span class="hljs-string">&#x27;r&#x27;</span>, <span class="hljs-string">&#x27;s&#x27;</span>, <span class="hljs-string">&#x27;t&#x27;</span>, <span class="hljs-string">&#x27;u&#x27;</span>, <span class="hljs-string">&#x27;v&#x27;</span>, <span class="hljs-string">&#x27;w&#x27;</span>, <span class="hljs-string">&#x27;y&#x27;</span>, <span class="hljs-string">&#x27;z&#x27;</span>, <span class="hljs-string">&#x27;Ġ&#x27;</span>, <span class="hljs-string">&#x27;Ġt&#x27;</span>, <span class="hljs-string">&#x27;is&#x27;</span>, <span class="hljs-string">&#x27;er&#x27;</span>, <span class="hljs-string">&#x27;Ġa&#x27;</span>, <span class="hljs-string">&#x27;Ġto&#x27;</span>, <span class="hljs-string">&#x27;en&#x27;</span>, <span class="hljs-string">&#x27;Th&#x27;</span>, <span class="hljs-string">&#x27;This&#x27;</span>, <span class="hljs-string">&#x27;ou&#x27;</span>, <span class="hljs-string">&#x27;se&#x27;</span>,
 <span class="hljs-string">&#x27;Ġtok&#x27;</span>, <span class="hljs-string">&#x27;Ġtoken&#x27;</span>, <span class="hljs-string">&#x27;nd&#x27;</span>, <span class="hljs-string">&#x27;Ġis&#x27;</span>, <span class="hljs-string">&#x27;Ġth&#x27;</span>, <span class="hljs-string">&#x27;Ġthe&#x27;</span>, <span class="hljs-string">&#x27;in&#x27;</span>, <span class="hljs-string">&#x27;Ġab&#x27;</span>, <span class="hljs-string">&#x27;Ġtokeni&#x27;</span>]<!-- HTML_TAG_END --></pre></div>


<div class="course-tip  bg-gradient-to-br dark:bg-gradient-to-r before:border-green-500 dark:before:border-green-800 from-green-50 dark:from-gray-900 to-white dark:to-gray-950 border border-green-50 text-green-700 dark:text-gray-400"><p>💡 在同一语料库上使用 <code>train_new_from_iterator()</code> 不会产生完全相同的词汇表。这是因为当有最频繁对的选择时,我们选择遇到的第一个, 而 🤗 Tokenizers 库根据内部ID选择第一个。</p></div>
<p>为了对新文本进行分词,我们对其进行预分词、拆分，然后应用学到的所有合并规则:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
	Copied</div></button></div>
	<pre><!-- HTML_TAG_START --><span class="hljs-keyword">def</span> <span class="hljs-title function_">tokenize</span>(<span class="hljs-params">text</span>):
    pre_tokenize_result = tokenizer._tokenizer.pre_tokenizer.pre_tokenize_str(text)
    pre_tokenized_text = [word <span class="hljs-keyword">for</span> word, offset <span class="hljs-keyword">in</span> pre_tokenize_result]
    splits = [[l <span class="hljs-keyword">for</span> l <span class="hljs-keyword">in</span> word] <span class="hljs-keyword">for</span> word <span class="hljs-keyword">in</span> pre_tokenized_text]
    <span class="hljs-keyword">for</span> pair, merge <span class="hljs-keyword">in</span> merges.items():
        <span class="hljs-keyword">for</span> idx, split <span class="hljs-keyword">in</span> <span class="hljs-built_in">enumerate</span>(splits):
            i = <span class="hljs-number">0</span>
            <span class="hljs-keyword">while</span> i &lt; <span class="hljs-built_in">len</span>(split) - <span class="hljs-number">1</span>:
                <span class="hljs-keyword">if</span> split[i] == pair[<span class="hljs-number">0</span>] <span class="hljs-keyword">and</span> split[i + <span class="hljs-number">1</span>] == pair[<span class="hljs-number">1</span>]:
                    split = split[:i] + [merge] + split[i + <span class="hljs-number">2</span> :]
                <span class="hljs-keyword">else</span>:
                    i += <span class="hljs-number">1</span>
            splits[idx] = split

    <span class="hljs-keyword">return</span> <span class="hljs-built_in">sum</span>(splits, [])<!-- HTML_TAG_END --></pre></div>
<p>我们可以在任何由字母表中的字符组成的文本上尝试这个:</p>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
	Copied</div></button></div>
	<pre><!-- HTML_TAG_START -->tokenize(<span class="hljs-string">&quot;This is not a token.&quot;</span>)<!-- HTML_TAG_END --></pre></div>

	<div class="code-block relative"><div class="absolute top-2.5 right-4"><button class="inline-flex items-center relative text-sm focus:text-green-500 cursor-pointer focus:outline-none transition duration-200 ease-in-out opacity-0 mx-0.5   text-gray-600 " title="code excerpt" type="button"><svg class="" xmlns="http://www.w3.org/2000/svg" aria-hidden="true" fill="currentColor" focusable="false" role="img" width="1em" height="1em" preserveAspectRatio="xMidYMid meet" viewBox="0 0 32 32"><path d="M28,10V28H10V10H28m0-2H10a2,2,0,0,0-2,2V28a2,2,0,0,0,2,2H28a2,2,0,0,0,2-2V10a2,2,0,0,0-2-2Z" transform="translate(0)"></path><path d="M4,18H2V4A2,2,0,0,1,4,2H18V4H4Z" transform="translate(0)"></path><rect fill="none" width="32" height="32"></rect></svg>
	<div class="absolute pointer-events-none transition-opacity bg-black text-white py-1 px-2 leading-tight rounded font-normal shadow left-1/2 top-full transform -translate-x-1/2 translate-y-2 opacity-0"><div class="absolute bottom-full left-1/2 transform -translate-x-1/2 w-0 h-0 border-black border-4 border-t-0" style="border-left-color: transparent; border-right-color: transparent; "></div>
	Copied</div></button></div>
	<pre><!-- HTML_TAG_START -->[<span class="hljs-string">&#x27;This&#x27;</span>, <span class="hljs-string">&#x27;Ġis&#x27;</span>, <span class="hljs-string">&#x27;Ġ&#x27;</span>, <span class="hljs-string">&#x27;n&#x27;</span>, <span class="hljs-string">&#x27;o&#x27;</span>, <span class="hljs-string">&#x27;t&#x27;</span>, <span class="hljs-string">&#x27;Ġa&#x27;</span>, <span class="hljs-string">&#x27;Ġtoken&#x27;</span>, <span class="hljs-string">&#x27;.&#x27;</span>]<!-- HTML_TAG_END --></pre></div>


<div class="course-tip course-tip-orange bg-gradient-to-br dark:bg-gradient-to-r before:border-orange-500 dark:before:border-orange-800 from-orange-50 dark:from-gray-900 to-white dark:to-gray-950 border border-orange-50 text-orange-700 dark:text-gray-400"><p>⚠️ 如果存在未知字符,我们的实现将抛出错误,因为我们没有做任何处理它们。GPT-2 实际上没有未知标记(使用字节级 BPE 时不可能得到未知字符),但这可能发生在这里,因为我们没有在初始词汇表中包含所有可能的字节。 BPE 的这方面超出了本节的范围,因此我们忽略了细节。</p></div>
<p>这就是 BPE 算法！接下来,我们将看看 WordPiece。</p>


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