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<h1 id="">逐块地构建标记器</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>正如我们在前几节中看到的，标记化包括几个步骤：</p>
<ul><li>规范化（任何认为必要的文本清理，例如删除空格或重音符号、Unicode 规范化等） </li>
<li>预标记化（将输入拆分为单词） </li>
<li>通过模型处理输入（使用预先拆分的词来生成一系列标记） </li>
<li>后处理（添加标记器的特殊标记，生成注意力掩码和标记类型 ID） </li></ul>
<p>提醒一下，这里再看一下整个过程</p>
<div class="flex justify-center"><img class="block dark:hidden" src="https://huggingface.co/datasets/huggingface-course/documentation-images/resolve/main/en/chapter6/tokenization_pipeline.svg" alt="The tokenization pipeline.">
<img class="hidden dark:block" src="https://huggingface.co/datasets/huggingface-course/documentation-images/resolve/main/en/chapter6/tokenization_pipeline-dark.svg" alt="The tokenization pipeline."></div>
<p>🤗 Tokenizers 库旨在为每个步骤提供多个选项，您可以将它们混合和匹配在一起。在本节中，我们将看到如何从头开始构建标记器，而不是像我们<a href="/course/chapter6/2">第二节 2</a>那样从旧的标记器训练新的标记器.然后，您将能够构建您能想到的任何类型的标记器！</p>
<iframe class="w-full xl:w-4/6 h-80" src="https://www.youtube-nocookie.com/embed/MR8tZm5ViWU" title="YouTube video player" frameborder="0" allow="accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>
<p>更准确地说，该库是围绕一个中央“Tokenizer”类构建的，构建这个类的每一部分可以在子模块的列表中重新组合：</p>
<ul><li><code>normalizers</code> 包含你可以使用的所有可能的Normalizer类型（完整列表<a href="https://huggingface.co/docs/tokenizers/python/latest/api/reference.html#module-tokenizers.normalizers" rel="nofollow">在这里</a>）。 </li>
<li><code>pre_tokenizesr</code> 包含您可以使用的所有可能的PreTokenizer类型（完整列表<a href="https://huggingface.co/docs/tokenizers/python/latest/api/reference.html#module-tokenizers.pre_tokenizers" rel="nofollow">在这里</a>）。 </li>
<li><code>models</code> 包含您可以使用的各种类型的Model，如BPE、WordPiece和Unigram（完整列表<a href="https://huggingface.co/docs/tokenizers/python/latest/api/reference.html#module-tokenizers.models" rel="nofollow">在这里</a>）。  </li>
<li><code>trainers</code> 包含所有不同类型的 trainer，你可以使用一个语料库训练你的模型（每种模型一个；完整列表<a href="https://huggingface.co/docs/tokenizers/python/latest/api/reference.html#module-tokenizers.trainers" rel="nofollow">在这里</a>）。 </li>
<li><code>post_processors</code> 包含你可以使用的各种类型的PostProcessor（完整列表<a href="https://huggingface.co/docs/tokenizers/python/latest/api/reference.html#module-tokenizers.processors" rel="nofollow">在这里</a>）。 </li>
<li><code>decoders</code> 包含各种类型的Decoder，可以用来解码标记化的输出（完整列表<a href="https://huggingface.co/docs/tokenizers/python/latest/components.html#decoders" rel="nofollow">在这里</a>）。 </li></ul>
<p>您可以<a href="https://huggingface.co/docs/tokenizers/python/latest/components.html" rel="nofollow">在这里</a>找到完整的模块列表。</p>
<h2 id="">获取语​​料库</h2>
<p>为了训练我们的新标记器，我们将使用一个小的文本语料库（因此示例运行得很快）。获取语​​料库的步骤与我们在[在这章的开始]((/course/chapter6/2)那一小节，但这次我们将使用<a href="https://huggingface.co/datasets/wikitext" rel="nofollow">WikiText-2</a>数据集：</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-keyword">from</span> datasets <span class="hljs-keyword">import</span> load_dataset

dataset = load_dataset(<span class="hljs-string">&quot;wikitext&quot;</span>, name=<span class="hljs-string">&quot;wikitext-2-raw-v1&quot;</span>, split=<span class="hljs-string">&quot;train&quot;</span>)


<span class="hljs-keyword">def</span> <span class="hljs-title function_">get_training_corpus</span>():
    <span class="hljs-keyword">for</span> i <span class="hljs-keyword">in</span> <span class="hljs-built_in">range</span>(<span class="hljs-number">0</span>, <span class="hljs-built_in">len</span>(dataset), <span class="hljs-number">1000</span>):
        <span class="hljs-keyword">yield</span> dataset[i : i + <span class="hljs-number">1000</span>][<span class="hljs-string">&quot;text&quot;</span>]<!-- HTML_TAG_END --></pre></div>
<p><strong>get_training_corpus()</strong> 函数是一个生成器，每次调用的时候将产生 1,000 个文本，我们将用它来训练标记器。</p>
<p>🤗 Tokenizers 也可以直接在文本文件上进行训练。以下是我们如何生成一个文本文件，其中包含我们可以在本地使用的来自 WikiText-2 的所有文本/输入：</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">with</span> <span class="hljs-built_in">open</span>(<span class="hljs-string">&quot;wikitext-2.txt&quot;</span>, <span class="hljs-string">&quot;w&quot;</span>, encoding=<span class="hljs-string">&quot;utf-8&quot;</span>) <span class="hljs-keyword">as</span> f:
    <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>(dataset)):
        f.write(dataset[i][<span class="hljs-string">&quot;text&quot;</span>] + <span class="hljs-string">&quot;\n&quot;</span>)<!-- HTML_TAG_END --></pre></div>
<p>接下来，我们将向您展示如何逐块构建您自己的 BERT、GPT-2 和 XLNet 标记器。这将为我们提供三个主要标记化算法的示例：WordPiece、BPE 和 Unigram。让我们从 BERT 开始吧！</p>
<h2 class="relative group"><a id="wordpiece" 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="#wordpiece"><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>从头开始构建 WordPiece 标记器
	</span></h2>

<p>要使用 🤗 Tokenizers 库构建标记器，我们首先使用<strong>model</strong>实例化一个 <strong>Tokenizer</strong> 对象与  ，然后将 <strong>normalizer</strong> , <strong>pre_tokenizer</strong> , <strong>post_processor</strong> ， 和 <strong>decoder</strong> 属性设置成我们想要的值。</p>
<p>对于这个例子，我们将创建一个 <strong>Tokenizer</strong> 使用 WordPiece 模型：</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">from</span> tokenizers <span class="hljs-keyword">import</span> (
    decoders,
    models,
    normalizers,
    pre_tokenizers,
    processors,
    trainers,
    Tokenizer,
)

tokenizer = Tokenizer(models.WordPiece(unk_token=<span class="hljs-string">&quot;[UNK]&quot;</span>))<!-- HTML_TAG_END --></pre></div>
<p>我们必须指定 <strong>unk_token</strong> 这样模型才知道当它遇到以前没有见过的字符时要返回什么。我们可以在此处设置的其他参数包括我们模型的<strong>vocab（字典）</strong>（我们将训练模型，所以我们不需要设置它）和 <strong>max_input_chars_per_word</strong> 即每个单词的最大长度（比传递的值长的单词将被拆分）</p>
<p>标记化的第一步是规范化，所以让我们从它开始。 由于 BERT 被广泛使用，所以有一个可以使用的 <code>BertNormalizer</code>，我们可以为 BERT 设置经典的选项：<code>lowercase（小写）</code> 和 <code>strip_accents（去除音调）</code>，不言自明； <code>clean_text</code> 删除所有控制字符并将重复的空格替换为一个； 和 <code>handle_chinese_chars</code>，在汉字周围放置空格。 要实现 <code>bert-base-uncased</code> ，我们可以这样设置这个规范器：</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>
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	<pre><!-- HTML_TAG_START -->tokenizer.normalizer = normalizers.BertNormalizer(lowercase=<span class="hljs-literal">True</span>)<!-- HTML_TAG_END --></pre></div>
<p>然而，一般来说，在构建新的标记器时，您可以使用已经在 🤗 Tokenizers库中实现的非常方便的normalizer——所以让我们看看如何手动创建 BERT normalizer。 该库提供了一个“Lowercase（小写）”的normalizer和一个“StripAccents”的normalizer，您可以使用“序列”组合多个normalizer：</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 -->tokenizer.normalizer = normalizers.<span class="hljs-type">Sequence</span>(
    [normalizers.NFD(), normalizers.Lowercase(), normalizers.StripAccents()]
)<!-- HTML_TAG_END --></pre></div>
<p>我们也在使用 <strong>NFD</strong> Unicode normalizer，否则 <strong>StripAccents</strong> normalizer 无法正确识别带重音的字符，因此没办法删除它们。</p>
<p>正如我们之前看到的，我们可以使用 <strong>normalize</strong> 的 <strong>normalize_str()</strong> 方法查看它对给定文本的影响：</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-built_in">print</span>(tokenizer.normalizer.normalize_str(<span class="hljs-string">&quot;Héllò hôw are ü?&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>
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	<pre><!-- HTML_TAG_START -->hello how are u?<!-- 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><strong>更进一步</strong>如果您在包含 unicode 字符的字符串上测试先前normalizers的两个版本，您肯定会注意到这两个normalizers并不完全等效。
为了不过度使用 <code>normalizers.Sequence</code> 使版本过于复杂，我们没有包含当 <code>clean_text</code> 参数设置为 <code>True</code> 时 <code>BertNormalizer</code> 需要的正则表达式替换 - 这是默认行为。 但不要担心：通过在normalizer序列中添加两个 <code>normalizers.Replace</code> 可以在不使用方便的 <code>BertNormalizer</code> 的情况下获得完全相同的规范化。</p></div>
<p>接下来是预标记步骤。 同样，我们可以使用一个预构建的“BertPreTokenizer”：</p>

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	<pre><!-- HTML_TAG_START -->tokenizer.pre_tokenizer = pre_tokenizers.BertPreTokenizer()<!-- HTML_TAG_END --></pre></div>
<p>或者我们可以从头开始构建它：</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>
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	<pre><!-- HTML_TAG_START -->tokenizer.pre_tokenizer = pre_tokenizers.Whitespace()<!-- HTML_TAG_END --></pre></div>
<p>请注意，<code>Whitespace</code> 预标记器会在空格和所有非字母、数字或下划线字符的字符上进行拆分，因此在本次的例子中上会根据空格和标点符号进行拆分：</p>

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	<pre><!-- HTML_TAG_START -->tokenizer.pre_tokenizer.pre_tokenize_str(<span class="hljs-string">&quot;Let&#x27;s test my pre-tokenizer.&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>
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	<pre><!-- HTML_TAG_START -->[(<span class="hljs-string">&#x27;Let&#x27;</span>, (<span class="hljs-number">0</span>, <span class="hljs-number">3</span>)), (<span class="hljs-string">&quot;&#x27;&quot;</span>, (<span class="hljs-number">3</span>, <span class="hljs-number">4</span>)), (<span class="hljs-string">&#x27;s&#x27;</span>, (<span class="hljs-number">4</span>, <span class="hljs-number">5</span>)), (<span class="hljs-string">&#x27;test&#x27;</span>, (<span class="hljs-number">6</span>, <span class="hljs-number">10</span>)), (<span class="hljs-string">&#x27;my&#x27;</span>, (<span class="hljs-number">11</span>, <span class="hljs-number">13</span>)), (<span class="hljs-string">&#x27;pre&#x27;</span>, (<span class="hljs-number">14</span>, <span class="hljs-number">17</span>)),
 (<span class="hljs-string">&#x27;-&#x27;</span>, (<span class="hljs-number">17</span>, <span class="hljs-number">18</span>)), (<span class="hljs-string">&#x27;tokenizer&#x27;</span>, (<span class="hljs-number">18</span>, <span class="hljs-number">27</span>)), (<span class="hljs-string">&#x27;.&#x27;</span>, (<span class="hljs-number">27</span>, <span class="hljs-number">28</span>))]<!-- HTML_TAG_END --></pre></div>
<p>如果您只想在空白处进行拆分，则应使用 <strong>WhitespaceSplit</strong> 代替预标记器：</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>
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	<pre><!-- HTML_TAG_START -->pre_tokenizer = pre_tokenizers.WhitespaceSplit()
pre_tokenizer.pre_tokenize_str(<span class="hljs-string">&quot;Let&#x27;s test my pre-tokenizer.&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>
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	<pre><!-- HTML_TAG_START -->[(<span class="hljs-string">&quot;Let&#x27;s&quot;</span>, (<span class="hljs-number">0</span>, <span class="hljs-number">5</span>)), (<span class="hljs-string">&#x27;test&#x27;</span>, (<span class="hljs-number">6</span>, <span class="hljs-number">10</span>)), (<span class="hljs-string">&#x27;my&#x27;</span>, (<span class="hljs-number">11</span>, <span class="hljs-number">13</span>)), (<span class="hljs-string">&#x27;pre-tokenizer.&#x27;</span>, (<span class="hljs-number">14</span>, <span class="hljs-number">28</span>))]<!-- HTML_TAG_END --></pre></div>
<p>像normalizers一样，您可以使用 <strong>Sequence</strong> 组成几个预标记器：</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>
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	<pre><!-- HTML_TAG_START -->pre_tokenizer = pre_tokenizers.<span class="hljs-type">Sequence</span>(
    [pre_tokenizers.WhitespaceSplit(), pre_tokenizers.Punctuation()]
)
pre_tokenizer.pre_tokenize_str(<span class="hljs-string">&quot;Let&#x27;s test my pre-tokenizer.&quot;</span>)<!-- HTML_TAG_END --></pre></div>

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	<pre><!-- HTML_TAG_START -->[(<span class="hljs-string">&#x27;Let&#x27;</span>, (<span class="hljs-number">0</span>, <span class="hljs-number">3</span>)), (<span class="hljs-string">&quot;&#x27;&quot;</span>, (<span class="hljs-number">3</span>, <span class="hljs-number">4</span>)), (<span class="hljs-string">&#x27;s&#x27;</span>, (<span class="hljs-number">4</span>, <span class="hljs-number">5</span>)), (<span class="hljs-string">&#x27;test&#x27;</span>, (<span class="hljs-number">6</span>, <span class="hljs-number">10</span>)), (<span class="hljs-string">&#x27;my&#x27;</span>, (<span class="hljs-number">11</span>, <span class="hljs-number">13</span>)), (<span class="hljs-string">&#x27;pre&#x27;</span>, (<span class="hljs-number">14</span>, <span class="hljs-number">17</span>)),
 (<span class="hljs-string">&#x27;-&#x27;</span>, (<span class="hljs-number">17</span>, <span class="hljs-number">18</span>)), (<span class="hljs-string">&#x27;tokenizer&#x27;</span>, (<span class="hljs-number">18</span>, <span class="hljs-number">27</span>)), (<span class="hljs-string">&#x27;.&#x27;</span>, (<span class="hljs-number">27</span>, <span class="hljs-number">28</span>))]<!-- HTML_TAG_END --></pre></div>
<p>标记化管道的下一步是输入给模型。我们已经在初始化中指定了我们的模型，但我们仍然需要训练它，这将需要一个 <strong>WordPieceTrainer</strong> .在 🤗 Tokenizers 中实例化训练器时要记住的主要事情是，您需要将您打算使用的所有特殊标记传递给它 - 否则它不会将它们添加到词汇表中，因为它们不在训练语料库中：</p>

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	<pre><!-- HTML_TAG_START -->special_tokens = [<span class="hljs-string">&quot;[UNK]&quot;</span>, <span class="hljs-string">&quot;[PAD]&quot;</span>, <span class="hljs-string">&quot;[CLS]&quot;</span>, <span class="hljs-string">&quot;[SEP]&quot;</span>, <span class="hljs-string">&quot;[MASK]&quot;</span>]
trainer = trainers.WordPieceTrainer(vocab_size=<span class="hljs-number">25000</span>, special_tokens=special_tokens)<!-- HTML_TAG_END --></pre></div>
<p>以及指定 <strong>vocab_size（词典大小）</strong> 和 <strong>special_tokens（特殊的标记）</strong> ，我们可以设置 <strong>min_frequency</strong> （记号必须出现在词汇表中的次数）或更改 <strong>continuing_subword_prefix</strong> （如果我们想使用与 <strong>##</strong>指代存在与字词相同的前缀 ）。</p>
<p>要使用我们之前定义的迭代器训练我们的模型，我们只需要执行以下命令：</p>

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	<pre><!-- HTML_TAG_START -->tokenizer.train_from_iterator(get_training_corpus(), trainer=trainer)<!-- HTML_TAG_END --></pre></div>
<p>我们还可以使用文本文件来训练我们的标记器，它看起来像这样（我们需要先初始化一个空的 <strong>WordPiece</strong> ）：</p>

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	<pre><!-- HTML_TAG_START -->tokenizer.model = models.WordPiece(unk_token=<span class="hljs-string">&quot;[UNK]&quot;</span>)
tokenizer.train([<span class="hljs-string">&quot;wikitext-2.txt&quot;</span>], trainer=trainer)<!-- HTML_TAG_END --></pre></div>
<p>在这两种情况下，我们都可以通过调用文本来测试标记器 <strong>encode()</strong> 方法：</p>

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	<pre><!-- HTML_TAG_START -->encoding = tokenizer.encode(<span class="hljs-string">&quot;Let&#x27;s test this tokenizer.&quot;</span>)
<span class="hljs-built_in">print</span>(encoding.tokens)<!-- HTML_TAG_END --></pre></div>

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	<pre><!-- HTML_TAG_START -->[<span class="hljs-string">&#x27;let&#x27;</span>, <span class="hljs-string">&quot;&#x27;&quot;</span>, <span class="hljs-string">&#x27;s&#x27;</span>, <span class="hljs-string">&#x27;test&#x27;</span>, <span class="hljs-string">&#x27;this&#x27;</span>, <span class="hljs-string">&#x27;tok&#x27;</span>, <span class="hljs-string">&#x27;##eni&#x27;</span>, <span class="hljs-string">&#x27;##zer&#x27;</span>, <span class="hljs-string">&#x27;.&#x27;</span>]<!-- HTML_TAG_END --></pre></div>
<p>这个 <strong>encoding</strong> 获得的是一个 <strong>Encoding</strong>对象 ，它的属性中包含标记器的所有必要输出： <strong>ids</strong> , <strong>type_ids</strong> , <strong>tokens</strong> , <strong>offsets</strong> , <strong>attention_mask</strong> , <strong>special_tokens_mask</strong> ， 和 <strong>overflowing</strong> .</p>
<p>标记化管道的最后一步是后处理。我们需要添加 <strong>[CLS]</strong> 开头的标记和 <strong>[SEP]</strong> 标记在末尾（或在每个句子之后，如果我们有一对句子）。我们将使用一个 <strong>TemplateProcessor</strong> 为此，但首先我们需要知道 <strong>[CLS]</strong> 和 <strong>[SEP]</strong> 在词汇表中的ID：</p>

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	<pre><!-- HTML_TAG_START -->cls_token_id = tokenizer.token_to_id(<span class="hljs-string">&quot;[CLS]&quot;</span>)
sep_token_id = tokenizer.token_to_id(<span class="hljs-string">&quot;[SEP]&quot;</span>)
<span class="hljs-built_in">print</span>(cls_token_id, sep_token_id)<!-- HTML_TAG_END --></pre></div>

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	<pre><!-- HTML_TAG_START -->(<span class="hljs-number">2</span>, <span class="hljs-number">3</span>)<!-- HTML_TAG_END --></pre></div>
<p>为了给 <strong>TemplateProcessor</strong> 编写模板，我们必须指定如何处理单个句子和一对句子。对于两者，我们都编写了我们想要使用的特殊标记；第一个（或单个）句子表示为 <strong>$A</strong> ，而第二个句子（如果对一对进行编码）表示为 <strong>$B</strong> .对于这些特殊标记和句子，我们还需要使用在冒号后指定相应的标记类型 ID。</p>
<p>因此经典的 BERT 模板定义如下：</p>

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	<pre><!-- HTML_TAG_START -->tokenizer.post_processor = processors.TemplateProcessing(
    single=<span class="hljs-string">f&quot;[CLS]:0 $A:0 [SEP]:0&quot;</span>,
    pair=<span class="hljs-string">f&quot;[CLS]:0 $A:0 [SEP]:0 $B:1 [SEP]:1&quot;</span>,
    special_tokens=[(<span class="hljs-string">&quot;[CLS]&quot;</span>, cls_token_id), (<span class="hljs-string">&quot;[SEP]&quot;</span>, sep_token_id)],
)<!-- HTML_TAG_END --></pre></div>
<p>请注意，我们需要传递特殊标记的 ID，以便标记器可以正确地将特殊标记转换为它们的 ID。</p>
<p>添加后，我们之前的示例将输出出：</p>

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	<pre><!-- HTML_TAG_START -->encoding = tokenizer.encode(<span class="hljs-string">&quot;Let&#x27;s test this tokenizer.&quot;</span>)
<span class="hljs-built_in">print</span>(encoding.tokens)<!-- HTML_TAG_END --></pre></div>

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	<pre><!-- HTML_TAG_START -->[<span class="hljs-string">&#x27;[CLS]&#x27;</span>, <span class="hljs-string">&#x27;let&#x27;</span>, <span class="hljs-string">&quot;&#x27;&quot;</span>, <span class="hljs-string">&#x27;s&#x27;</span>, <span class="hljs-string">&#x27;test&#x27;</span>, <span class="hljs-string">&#x27;this&#x27;</span>, <span class="hljs-string">&#x27;tok&#x27;</span>, <span class="hljs-string">&#x27;##eni&#x27;</span>, <span class="hljs-string">&#x27;##zer&#x27;</span>, <span class="hljs-string">&#x27;.&#x27;</span>, <span class="hljs-string">&#x27;[SEP]&#x27;</span>]<!-- HTML_TAG_END --></pre></div>
<p>在一对句子中，我们得到了正确的结果：</p>

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	<pre><!-- HTML_TAG_START -->encoding = tokenizer.encode(<span class="hljs-string">&quot;Let&#x27;s test this tokenizer...&quot;</span>, <span class="hljs-string">&quot;on a pair of sentences.&quot;</span>)
<span class="hljs-built_in">print</span>(encoding.tokens)
<span class="hljs-built_in">print</span>(encoding.type_ids)<!-- HTML_TAG_END --></pre></div>

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	<pre><!-- HTML_TAG_START -->[<span class="hljs-string">&#x27;[CLS]&#x27;</span>, <span class="hljs-string">&#x27;let&#x27;</span>, <span class="hljs-string">&quot;&#x27;&quot;</span>, <span class="hljs-string">&#x27;s&#x27;</span>, <span class="hljs-string">&#x27;test&#x27;</span>, <span class="hljs-string">&#x27;this&#x27;</span>, <span class="hljs-string">&#x27;tok&#x27;</span>, <span class="hljs-string">&#x27;##eni&#x27;</span>, <span class="hljs-string">&#x27;##zer&#x27;</span>, <span class="hljs-string">&#x27;...&#x27;</span>, <span class="hljs-string">&#x27;[SEP]&#x27;</span>, <span class="hljs-string">&#x27;on&#x27;</span>, <span class="hljs-string">&#x27;a&#x27;</span>, <span class="hljs-string">&#x27;pair&#x27;</span>, <span class="hljs-string">&#x27;of&#x27;</span>, <span class="hljs-string">&#x27;sentences&#x27;</span>, <span class="hljs-string">&#x27;.&#x27;</span>, <span class="hljs-string">&#x27;[SEP]&#x27;</span>]
[<span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>]<!-- HTML_TAG_END --></pre></div>
<p>我们几乎从头开始构建了这个标记器——但是还有最后一步是指定一个解码器：</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>
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	<pre><!-- HTML_TAG_START -->tokenizer.decoder = decoders.WordPiece(prefix=<span class="hljs-string">&quot;##&quot;</span>)<!-- HTML_TAG_END --></pre></div>
<p>让我们测试一下我们之前的 <strong>encoding</strong> ：</p>

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	<pre><!-- HTML_TAG_START -->tokenizer.decode(encoding.ids)<!-- HTML_TAG_END --></pre></div>

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	<pre><!-- HTML_TAG_START --><span class="hljs-string">&quot;let&#x27;s test this tokenizer... on a pair of sentences.&quot;</span><!-- HTML_TAG_END --></pre></div>
<p>很好！我们可以将标记器保存在一个 JSON 文件中，如下所示：</p>

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	<pre><!-- HTML_TAG_START -->tokenizer.save(<span class="hljs-string">&quot;tokenizer.json&quot;</span>)<!-- HTML_TAG_END --></pre></div>
<p>然后我们可以使用<strong>from_file()</strong> 方法从该文件里重新加载 <strong>Tokenizer</strong> 对象：</p>

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	<pre><!-- HTML_TAG_START -->new_tokenizer = Tokenizer.from_file(<span class="hljs-string">&quot;tokenizer.json&quot;</span>)<!-- HTML_TAG_END --></pre></div>
<p>要在 🤗 Transformers 中使用这个标记器，我们必须将它包裹在一个 <strong>PreTrainedTokenizerFast</strong> 类中。我们可以使用泛型类，或者，如果我们的标记器对应于现有模型，则使用该类（例如这里的 <strong>BertTokenizerFast</strong> ）。如果您应用本课来构建全新的标记器，则必须使用第一个选项。</p>
<p>要将标记器包装在 <code>PreTrainedTokenizerFast</code> 类中，我们可以将我们构建的标记器作为<code>tokenizer_object</code> 传递，或者将我们保存为<code>tokenizer_file</code> 的标记器文件传递。 要记住的关键是我们必须手动设置所有特殊标记，因为该类无法从 <code>tokenizer</code> 对象推断出哪个标记是掩码标记、<code>[CLS]</code> 标记等：</p>

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	<pre><!-- HTML_TAG_START --><span class="hljs-keyword">from</span> transformers <span class="hljs-keyword">import</span> PreTrainedTokenizerFast

wrapped_tokenizer = PreTrainedTokenizerFast(
    tokenizer_object=tokenizer,
    <span class="hljs-comment"># tokenizer_file=&quot;tokenizer.json&quot;, # You can load from the tokenizer file, alternatively</span>
    unk_token=<span class="hljs-string">&quot;[UNK]&quot;</span>,
    pad_token=<span class="hljs-string">&quot;[PAD]&quot;</span>,
    cls_token=<span class="hljs-string">&quot;[CLS]&quot;</span>,
    sep_token=<span class="hljs-string">&quot;[SEP]&quot;</span>,
    mask_token=<span class="hljs-string">&quot;[MASK]&quot;</span>,
)<!-- HTML_TAG_END --></pre></div>
<p>如果您使用特定的标记器类（例如 <strong>BertTokenizerFast</strong> )，您只需要指定与默认标记不同的特殊标记（此处没有）：</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-keyword">from</span> transformers <span class="hljs-keyword">import</span> BertTokenizerFast

wrapped_tokenizer = BertTokenizerFast(tokenizer_object=tokenizer)<!-- HTML_TAG_END --></pre></div>
<p>然后，您可以像使用任何其他 🤗 Transformers 标记器一样使用此标记器。你可以用 <strong>save_pretrained()</strong> 方法，或使用 <strong>push_to_hub()</strong> 方法。</p>
<p>现在我们已经了解了如何构建 WordPiece 标记器，让我们对 BPE 标记器进行同样的操作。因为您已经知道了所有步骤，所以我们会进行地更快一点，并且只突出展示两者不一样的地方。</p>
<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>从头开始构建 BPE 标记器
	</span></h2>

<p>现在让我们构建一个 GPT-2 标记器。与 BERT 标记器一样，我们首先使用 <strong>Tokenizer</strong> 初始化一个BPE 模型：</p>

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	<pre><!-- HTML_TAG_START -->tokenizer = Tokenizer(models.BPE())<!-- HTML_TAG_END --></pre></div>
<p>和 BERT 一样，如果我们有一个词汇表，我们可以用一个词汇表来初始化这个模型（在这种情况下，我们需要传递 <code>vocab</code> 和 <code>merges</code>），但是由于我们将从头开始训练，所以我们不需要这样去做。 我们也不需要指定“unk_token”，因为 GPT-2 使用的字节级 BPE，不需要“unk_token”。</p>
<p>GPT-2 不使用归一化器，因此我们跳过该步骤并直接进入预标记化：</p>

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	<pre><!-- HTML_TAG_START -->tokenizer.pre_tokenizer = pre_tokenizers.ByteLevel(add_prefix_space=<span class="hljs-literal">False</span>)<!-- HTML_TAG_END --></pre></div>
<p>我们在此处添加到 <code>ByteLevel</code> 的选项是不在句子开头添加空格（默认为ture）。 我们可以看一下使用这个标记器对之前示例文本的预标记：</p>

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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 -->tokenizer.pre_tokenizer.pre_tokenize_str(<span class="hljs-string">&quot;Let&#x27;s test pre-tokenization!&quot;</span>)<!-- HTML_TAG_END --></pre></div>

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	<pre><!-- HTML_TAG_START -->[(<span class="hljs-string">&#x27;Let&#x27;</span>, (<span class="hljs-number">0</span>, <span class="hljs-number">3</span>)), (<span class="hljs-string">&quot;&#x27;s&quot;</span>, (<span class="hljs-number">3</span>, <span class="hljs-number">5</span>)), (<span class="hljs-string">&#x27;Ġtest&#x27;</span>, (<span class="hljs-number">5</span>, <span class="hljs-number">10</span>)), (<span class="hljs-string">&#x27;Ġpre&#x27;</span>, (<span class="hljs-number">10</span>, <span class="hljs-number">14</span>)), (<span class="hljs-string">&#x27;-&#x27;</span>, (<span class="hljs-number">14</span>, <span class="hljs-number">15</span>)),
 (<span class="hljs-string">&#x27;tokenization&#x27;</span>, (<span class="hljs-number">15</span>, <span class="hljs-number">27</span>)), (<span class="hljs-string">&#x27;!&#x27;</span>, (<span class="hljs-number">27</span>, <span class="hljs-number">28</span>))]<!-- HTML_TAG_END --></pre></div>
<p>接下来是需要训练的模型。对于 GPT-2，唯一的特殊标记是文本结束标记：</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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	<pre><!-- HTML_TAG_START -->trainer = trainers.BpeTrainer(vocab_size=<span class="hljs-number">25000</span>, special_tokens=[<span class="hljs-string">&quot;&lt;|endoftext|&gt;&quot;</span>])
tokenizer.train_from_iterator(get_training_corpus(), trainer=trainer)<!-- HTML_TAG_END --></pre></div>
<p>与 <code>WordPieceTrainer</code> 以及 <code>vocab_size</code> 和 <code>special_tokens</code> 一样，我们可以指定 <code>min_frequency</code> 如果我们愿意，或者如果我们有一个词尾后缀（如 <code>&lt;/w&gt;</code> )，我们可以使用 <code>end_of_word_suffix</code> 设置它。</p>
<p>这个标记器也可以在文本文件上训练：</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>
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	<pre><!-- HTML_TAG_START -->tokenizer.model = models.BPE()
tokenizer.train([<span class="hljs-string">&quot;wikitext-2.txt&quot;</span>], trainer=trainer)<!-- HTML_TAG_END --></pre></div>
<p>让我们看一下示例文本的标记化后的结果：</p>

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	<pre><!-- HTML_TAG_START -->encoding = tokenizer.encode(<span class="hljs-string">&quot;Let&#x27;s test this tokenizer.&quot;</span>)
<span class="hljs-built_in">print</span>(encoding.tokens)<!-- HTML_TAG_END --></pre></div>

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	<pre><!-- HTML_TAG_START -->[<span class="hljs-string">&#x27;L&#x27;</span>, <span class="hljs-string">&#x27;et&#x27;</span>, <span class="hljs-string">&quot;&#x27;&quot;</span>, <span class="hljs-string">&#x27;s&#x27;</span>, <span class="hljs-string">&#x27;Ġtest&#x27;</span>, <span class="hljs-string">&#x27;Ġthis&#x27;</span>, <span class="hljs-string">&#x27;Ġto&#x27;</span>, <span class="hljs-string">&#x27;ken&#x27;</span>, <span class="hljs-string">&#x27;izer&#x27;</span>, <span class="hljs-string">&#x27;.&#x27;</span>]<!-- HTML_TAG_END --></pre></div>
<p>我们对 GPT-2 标记器添加字节级后处理，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>
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	<pre><!-- HTML_TAG_START -->tokenizer.post_processor = processors.ByteLevel(trim_offsets=<span class="hljs-literal">False</span>)<!-- HTML_TAG_END --></pre></div>
<p><code>trim_offsets = False</code> 选项指示我们应该保留以 ‘Ġ’ 开头的标记的偏移量：这样偏移量的开头将指向单词之前的空格，而不是第一个单词的字符（因为空格在技术上是标记的一部分）。 让我们看看我们刚刚编码的文本的结果，其中 <code>&#39;Ġtest&#39;</code> 是索引第 4 处的标记：</p>

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	<pre><!-- HTML_TAG_START -->sentence = <span class="hljs-string">&quot;Let&#x27;s test this tokenizer.&quot;</span>
encoding = tokenizer.encode(sentence)
start, end = encoding.offsets[<span class="hljs-number">4</span>]
sentence[start:end]<!-- HTML_TAG_END --></pre></div>

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	<pre><!-- HTML_TAG_START --><span class="hljs-string">&#x27; test&#x27;</span><!-- HTML_TAG_END --></pre></div>
<p>最后，我们添加一个字节级解码器：</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>
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	<pre><!-- HTML_TAG_START -->tokenizer.decoder = decoders.ByteLevel()<!-- HTML_TAG_END --></pre></div>
<p>我们可以仔细检查它是否正常工作：</p>

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	<pre><!-- HTML_TAG_START -->tokenizer.decode(encoding.ids)<!-- HTML_TAG_END --></pre></div>

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	<pre><!-- HTML_TAG_START --><span class="hljs-string">&quot;Let&#x27;s test this tokenizer.&quot;</span><!-- HTML_TAG_END --></pre></div>
<p>很好！现在我们完成了，我们可以像以前一样保存标记器，并将它包装在一个 <strong>PreTrainedTokenizerFast</strong> 或者 <strong>GPT2TokenizerFast</strong> 如果我们想在 🤗 Transformers中使用它：</p>

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	<pre><!-- HTML_TAG_START --><span class="hljs-keyword">from</span> transformers <span class="hljs-keyword">import</span> PreTrainedTokenizerFast

wrapped_tokenizer = PreTrainedTokenizerFast(
    tokenizer_object=tokenizer,
    bos_token=<span class="hljs-string">&quot;&lt;|endoftext|&gt;&quot;</span>,
    eos_token=<span class="hljs-string">&quot;&lt;|endoftext|&gt;&quot;</span>,
)<!-- HTML_TAG_END --></pre></div>
<p>或者：</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-keyword">from</span> transformers <span class="hljs-keyword">import</span> GPT2TokenizerFast

wrapped_tokenizer = GPT2TokenizerFast(tokenizer_object=tokenizer)<!-- HTML_TAG_END --></pre></div>
<p>作为最后一个示例，我们将向您展示如何从头开始构建 Unigram 标记器。</p>
<h2 class="relative group"><a id="unigram" 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="#unigram"><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>从头开始构建 Unigram 标记器
	</span></h2>

<p>现在让我们构建一个 XLNet 标记器。与之前的标记器一样，我们首先使用 Unigram 模型初始化一个 <strong>Tokenizer</strong> ：</p>

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	<pre><!-- HTML_TAG_START -->tokenizer = Tokenizer(models.Unigram())<!-- HTML_TAG_END --></pre></div>
<p>同样，如果我们有词汇表，我们可以用词汇表初始化这个模型。</p>
<p>对于标准化，XLNet 使用了一些替换的方法（来自 SentencePiece）：</p>

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	<pre><!-- HTML_TAG_START --><span class="hljs-keyword">from</span> tokenizers <span class="hljs-keyword">import</span> Regex

tokenizer.normalizer = normalizers.<span class="hljs-type">Sequence</span>(
    [
        normalizers.Replace(<span class="hljs-string">&quot;``&quot;</span>, <span class="hljs-string">&#x27;&quot;&#x27;</span>),
        normalizers.Replace(<span class="hljs-string">&quot;&#x27;&#x27;&quot;</span>, <span class="hljs-string">&#x27;&quot;&#x27;</span>),
        normalizers.NFKD(),
        normalizers.StripAccents(),
        normalizers.Replace(Regex(<span class="hljs-string">&quot; {2,}&quot;</span>), <span class="hljs-string">&quot; &quot;</span>),
    ]
)<!-- HTML_TAG_END --></pre></div>
<p>这会取代 <strong>“</strong> 和 <strong>”</strong> 和 <strong>”</strong> 以及任何两个或多个空格与单个空格的序列，以及删除文本中的重音以进行标记。</p>
<p>用于任何 SentencePiece 标记器的预标记器是 <code>Metaspace</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>
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	<pre><!-- HTML_TAG_START -->tokenizer.pre_tokenizer = pre_tokenizers.Metaspace()<!-- HTML_TAG_END --></pre></div>
<p>我们可以像以前一样查看示例文本的预标记化：</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 -->tokenizer.pre_tokenizer.pre_tokenize_str(<span class="hljs-string">&quot;Let&#x27;s test the pre-tokenizer!&quot;</span>)<!-- HTML_TAG_END --></pre></div>

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	<pre><!-- HTML_TAG_START -->[(<span class="hljs-string">&quot;▁Let&#x27;s&quot;</span>, (<span class="hljs-number">0</span>, <span class="hljs-number">5</span>)), (<span class="hljs-string">&#x27;▁test&#x27;</span>, (<span class="hljs-number">5</span>, <span class="hljs-number">10</span>)), (<span class="hljs-string">&#x27;▁the&#x27;</span>, (<span class="hljs-number">10</span>, <span class="hljs-number">14</span>)), (<span class="hljs-string">&#x27;▁pre-tokenizer!&#x27;</span>, (<span class="hljs-number">14</span>, <span class="hljs-number">29</span>))]<!-- HTML_TAG_END --></pre></div>
<p>接下来是需要训练的模型。 XLNet 有不少特殊的标记：</p>

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	<pre><!-- HTML_TAG_START -->special_tokens = [<span class="hljs-string">&quot;&lt;cls&gt;&quot;</span>, <span class="hljs-string">&quot;&lt;sep&gt;&quot;</span>, <span class="hljs-string">&quot;&lt;unk&gt;&quot;</span>, <span class="hljs-string">&quot;&lt;pad&gt;&quot;</span>, <span class="hljs-string">&quot;&lt;mask&gt;&quot;</span>, <span class="hljs-string">&quot;&lt;s&gt;&quot;</span>, <span class="hljs-string">&quot;&lt;/s&gt;&quot;</span>]
trainer = trainers.UnigramTrainer(
    vocab_size=<span class="hljs-number">25000</span>, special_tokens=special_tokens, unk_token=<span class="hljs-string">&quot;&lt;unk&gt;&quot;</span>
)
tokenizer.train_from_iterator(get_training_corpus(), trainer=trainer)<!-- HTML_TAG_END --></pre></div>
<p>不要忘记<code>UnigramTrainer</code> 的一个非常重要的参数是<code>unk_token</code>。 我们还可以传递特定于 Unigram 算法的其他参数，例如删除标记的每个步骤的“shrinking_factor（收缩因子）”（默认为 0.75）或指定给定标记的最大长度的“max_piece_length”（默认为 16） .</p>
<p>这个标记器也可以在文本文件上训练：</p>

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	<pre><!-- HTML_TAG_START -->tokenizer.model = models.Unigram()
tokenizer.train([<span class="hljs-string">&quot;wikitext-2.txt&quot;</span>], trainer=trainer)<!-- HTML_TAG_END --></pre></div>
<p>让我们看一下示例文本的标记化后的结果：</p>

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	<pre><!-- HTML_TAG_START -->encoding = tokenizer.encode(<span class="hljs-string">&quot;Let&#x27;s test this tokenizer.&quot;</span>)
<span class="hljs-built_in">print</span>(encoding.tokens)<!-- HTML_TAG_END --></pre></div>

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	<pre><!-- HTML_TAG_START -->[<span class="hljs-string">&#x27;▁Let&#x27;</span>, <span class="hljs-string">&quot;&#x27;&quot;</span>, <span class="hljs-string">&#x27;s&#x27;</span>, <span class="hljs-string">&#x27;▁test&#x27;</span>, <span class="hljs-string">&#x27;▁this&#x27;</span>, <span class="hljs-string">&#x27;▁to&#x27;</span>, <span class="hljs-string">&#x27;ken&#x27;</span>, <span class="hljs-string">&#x27;izer&#x27;</span>, <span class="hljs-string">&#x27;.&#x27;</span>]<!-- HTML_TAG_END --></pre></div>
<p>A peculiarity of XLNet is that it puts the <code>&lt;cls&gt;</code> token at the end of the sentence, with a type ID of 2 (to distinguish it from the other tokens). It’s padding on the left, as a result. We can deal with all the special tokens and token type IDs with a template, like for BERT, but first we have to get the IDs of the <code>&lt;cls&gt;</code> and <code>&lt;sep&gt;</code> tokens:
XLNet 的一个特点是它将<code>&lt;cls&gt;</code> 标记放在句子的末尾，类型ID 为2（以将其与其他标记区分开来）。它会将结果填充在左侧。 我们可以使用模板处理所有特殊标记和标记类型 ID，例如 BERT，但首先我们必须获取 <code>&lt;cls&gt;</code> 和 <code>&lt;sep&gt;</code> 标记的 ID：</p>

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	<pre><!-- HTML_TAG_START -->cls_token_id = tokenizer.token_to_id(<span class="hljs-string">&quot;&lt;cls&gt;&quot;</span>)
sep_token_id = tokenizer.token_to_id(<span class="hljs-string">&quot;&lt;sep&gt;&quot;</span>)
<span class="hljs-built_in">print</span>(cls_token_id, sep_token_id)<!-- HTML_TAG_END --></pre></div>

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	<pre><!-- HTML_TAG_START --><span class="hljs-number">0</span> <span class="hljs-number">1</span><!-- HTML_TAG_END --></pre></div>
<p>模板如下所示：</p>

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	<pre><!-- HTML_TAG_START -->tokenizer.post_processor = processors.TemplateProcessing(
    single=<span class="hljs-string">&quot;$A:0 &lt;sep&gt;:0 &lt;cls&gt;:2&quot;</span>,
    pair=<span class="hljs-string">&quot;$A:0 &lt;sep&gt;:0 $B:1 &lt;sep&gt;:1 &lt;cls&gt;:2&quot;</span>,
    special_tokens=[(<span class="hljs-string">&quot;&lt;sep&gt;&quot;</span>, sep_token_id), (<span class="hljs-string">&quot;&lt;cls&gt;&quot;</span>, cls_token_id)],
)<!-- HTML_TAG_END --></pre></div>
<p>我们可以通过编码一对句子来测试它的工作原理：</p>

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	<pre><!-- HTML_TAG_START -->encoding = tokenizer.encode(<span class="hljs-string">&quot;Let&#x27;s test this tokenizer...&quot;</span>, <span class="hljs-string">&quot;on a pair of sentences!&quot;</span>)
<span class="hljs-built_in">print</span>(encoding.tokens)
<span class="hljs-built_in">print</span>(encoding.type_ids)<!-- HTML_TAG_END --></pre></div>

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	<pre><!-- HTML_TAG_START -->[<span class="hljs-string">&#x27;▁Let&#x27;</span>, <span class="hljs-string">&quot;&#x27;&quot;</span>, <span class="hljs-string">&#x27;s&#x27;</span>, <span class="hljs-string">&#x27;▁test&#x27;</span>, <span class="hljs-string">&#x27;▁this&#x27;</span>, <span class="hljs-string">&#x27;▁to&#x27;</span>, <span class="hljs-string">&#x27;ken&#x27;</span>, <span class="hljs-string">&#x27;izer&#x27;</span>, <span class="hljs-string">&#x27;.&#x27;</span>, <span class="hljs-string">&#x27;.&#x27;</span>, <span class="hljs-string">&#x27;.&#x27;</span>, <span class="hljs-string">&#x27;&lt;sep&gt;&#x27;</span>, <span class="hljs-string">&#x27;▁&#x27;</span>, <span class="hljs-string">&#x27;on&#x27;</span>, <span class="hljs-string">&#x27;▁&#x27;</span>, <span class="hljs-string">&#x27;a&#x27;</span>, <span class="hljs-string">&#x27;▁pair&#x27;</span>, 
  <span class="hljs-string">&#x27;▁of&#x27;</span>, <span class="hljs-string">&#x27;▁sentence&#x27;</span>, <span class="hljs-string">&#x27;s&#x27;</span>, <span class="hljs-string">&#x27;!&#x27;</span>, <span class="hljs-string">&#x27;&lt;sep&gt;&#x27;</span>, <span class="hljs-string">&#x27;&lt;cls&gt;&#x27;</span>]
[<span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">0</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">1</span>, <span class="hljs-number">2</span>]<!-- HTML_TAG_END --></pre></div>
<p>最后，我们添加一个 <strong>Metaspace</strong> 解码器：</p>

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	<pre><!-- HTML_TAG_START -->tokenizer.decoder = decoders.Metaspace()<!-- HTML_TAG_END --></pre></div>
<p>我们完成了这个标记器！ 我们可以像以前一样保存标记器，如果我们想在 🤗 Transformers 中使用它，可以将它包装在 <code>PreTrainedTokenizerFast</code> 或 <code>XLNetTokenizerFast</code> 中。 使用 <code>PreTrainedTokenizerFast</code> 时要注意的一件事是，我们需要告诉🤗 Transformers 库应该在左侧填充特殊标记：</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>
	<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">from</span> transformers <span class="hljs-keyword">import</span> PreTrainedTokenizerFast

wrapped_tokenizer = PreTrainedTokenizerFast(
    tokenizer_object=tokenizer,
    bos_token=<span class="hljs-string">&quot;&lt;s&gt;&quot;</span>,
    eos_token=<span class="hljs-string">&quot;&lt;/s&gt;&quot;</span>,
    unk_token=<span class="hljs-string">&quot;&lt;unk&gt;&quot;</span>,
    pad_token=<span class="hljs-string">&quot;&lt;pad&gt;&quot;</span>,
    cls_token=<span class="hljs-string">&quot;&lt;cls&gt;&quot;</span>,
    sep_token=<span class="hljs-string">&quot;&lt;sep&gt;&quot;</span>,
    mask_token=<span class="hljs-string">&quot;&lt;mask&gt;&quot;</span>,
    padding_side=<span class="hljs-string">&quot;left&quot;</span>,
)<!-- HTML_TAG_END --></pre></div>
<p>或者：</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">from</span> transformers <span class="hljs-keyword">import</span> XLNetTokenizerFast

wrapped_tokenizer = XLNetTokenizerFast(tokenizer_object=tokenizer)<!-- HTML_TAG_END --></pre></div>
<p>现在您已经了解了如何使用各种构建块来构建现有的标记器，您应该能够使用 🤗 tokenizer库编写您想要的任何标记器，并能够在 🤗 Transformers中使用它。</p>


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