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<meta charset="utf-8" /><meta name="hf:doc:metadata" content="{&quot;title&quot;:&quot;Tokenizers&quot;,&quot;local&quot;:&quot;tokenizers&quot;,&quot;sections&quot;:[{&quot;title&quot;:&quot;Load a tokenizer&quot;,&quot;local&quot;:&quot;load-a-tokenizer&quot;,&quot;sections&quot;:[],&quot;depth&quot;:2},{&quot;title&quot;:&quot;Encode and decode&quot;,&quot;local&quot;:&quot;encode-and-decode&quot;,&quot;sections&quot;:[],&quot;depth&quot;:2},{&quot;title&quot;:&quot;Special tokens&quot;,&quot;local&quot;:&quot;special-tokens&quot;,&quot;sections&quot;:[],&quot;depth&quot;:2},{&quot;title&quot;:&quot;Batch processing&quot;,&quot;local&quot;:&quot;batch-processing&quot;,&quot;sections&quot;:[{&quot;title&quot;:&quot;Padding&quot;,&quot;local&quot;:&quot;padding&quot;,&quot;sections&quot;:[],&quot;depth&quot;:3},{&quot;title&quot;:&quot;Truncation&quot;,&quot;local&quot;:&quot;truncation&quot;,&quot;sections&quot;:[],&quot;depth&quot;:3}],&quot;depth&quot;:2},{&quot;title&quot;:&quot;Backends&quot;,&quot;local&quot;:&quot;backends&quot;,&quot;sections&quot;:[],&quot;depth&quot;:2},{&quot;title&quot;:&quot;Inspect the tokenizer architecture&quot;,&quot;local&quot;:&quot;inspect-the-tokenizer-architecture&quot;,&quot;sections&quot;:[],&quot;depth&quot;:2},{&quot;title&quot;:&quot;Resources&quot;,&quot;local&quot;:&quot;resources&quot;,&quot;sections&quot;:[],&quot;depth&quot;:2}],&quot;depth&quot;:1}">
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 <link rel="modulepreload" href="/docs/transformers/pr_26617/en/_app/immutable/chunks/HfOption.fb051768.js"><!-- HEAD_svelte-u9bgzb_START --><meta name="hf:doc:metadata" content="{&quot;title&quot;:&quot;Tokenizers&quot;,&quot;local&quot;:&quot;tokenizers&quot;,&quot;sections&quot;:[{&quot;title&quot;:&quot;Load a tokenizer&quot;,&quot;local&quot;:&quot;load-a-tokenizer&quot;,&quot;sections&quot;:[],&quot;depth&quot;:2},{&quot;title&quot;:&quot;Encode and decode&quot;,&quot;local&quot;:&quot;encode-and-decode&quot;,&quot;sections&quot;:[],&quot;depth&quot;:2},{&quot;title&quot;:&quot;Special tokens&quot;,&quot;local&quot;:&quot;special-tokens&quot;,&quot;sections&quot;:[],&quot;depth&quot;:2},{&quot;title&quot;:&quot;Batch processing&quot;,&quot;local&quot;:&quot;batch-processing&quot;,&quot;sections&quot;:[{&quot;title&quot;:&quot;Padding&quot;,&quot;local&quot;:&quot;padding&quot;,&quot;sections&quot;:[],&quot;depth&quot;:3},{&quot;title&quot;:&quot;Truncation&quot;,&quot;local&quot;:&quot;truncation&quot;,&quot;sections&quot;:[],&quot;depth&quot;:3}],&quot;depth&quot;:2},{&quot;title&quot;:&quot;Backends&quot;,&quot;local&quot;:&quot;backends&quot;,&quot;sections&quot;:[],&quot;depth&quot;:2},{&quot;title&quot;:&quot;Inspect the tokenizer architecture&quot;,&quot;local&quot;:&quot;inspect-the-tokenizer-architecture&quot;,&quot;sections&quot;:[],&quot;depth&quot;:2},{&quot;title&quot;:&quot;Resources&quot;,&quot;local&quot;:&quot;resources&quot;,&quot;sections&quot;:[],&quot;depth&quot;:2}],&quot;depth&quot;:1}"><!-- HEAD_svelte-u9bgzb_END --> <p></p> <div class="items-center shrink-0 min-w-[100px] max-sm:min-w-[50px] justify-end ml-auto flex" style="float: right; margin-left: 10px; display: inline-flex; position: relative; z-index: 10;"><div class="inline-flex rounded-md max-sm:rounded-sm"><button class="inline-flex items-center gap-1 h-7 max-sm:h-7 px-2 max-sm:px-1.5 text-sm font-medium text-gray-800 border border-r-0 rounded-l-md max-sm:rounded-l-sm border-gray-200 bg-white hover:shadow-inner dark:border-gray-850 dark:bg-gray-950 dark:text-gray-200 dark:hover:bg-gray-800" aria-live="polite"><span class="inline-flex items-center justify-center rounded-md p-0.5 max-sm:p-0 hover:text-gray-800 dark:hover:text-gray-200"><svg class="sm:size-3.5 size-3" 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></span> <span>Copy page</span></button> <button class="inline-flex items-center justify-center w-6 max-sm:w-5 h-7 max-sm:h-7 disabled:pointer-events-none text-sm text-gray-500 hover:text-gray-700 dark:hover:text-white rounded-r-md max-sm:rounded-r-sm border border-l transition border-gray-200 bg-white hover:shadow-inner dark:border-gray-850 dark:bg-gray-950 dark:text-gray-200 dark:hover:bg-gray-800" aria-haspopup="menu" aria-expanded="false" aria-label="Open copy menu"><svg class="transition-transform text-gray-400 overflow-visible sm:size-3.5 size-3 rotate-0" width="1em" height="1em" viewBox="0 0 12 7" fill="none" xmlns="http://www.w3.org/2000/svg"><path d="M1 1L6 6L11 1" stroke="currentColor"></path></svg></button></div> </div> <h1 class="relative group"><a id="tokenizers" 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="#tokenizers"><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>Tokenizers</span></h1> <p data-svelte-h="svelte-ezsjwy">A tokenizer converts text into tensors, which are the inputs to a model. It normalizes and splits text, applies the tokenization algorithm, adds special tokens, and decodes output ids back into text.</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 class=""><!-- 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;google/gemma-2-2b&quot;</span>)
tokenizer(<span class="hljs-string">&quot;Sphinx of black quartz, judge my vow.&quot;</span>, return_tensors=<span class="hljs-string">&quot;pt&quot;</span>)
{
 <span class="hljs-string">&#x27;input_ids&#x27;</span>: tensor([[ <span class="hljs-number">2</span>, <span class="hljs-number">235277</span>, <span class="hljs-number">82913</span>, <span class="hljs-number">576</span>, <span class="hljs-number">2656</span>, <span class="hljs-number">30407</span>, <span class="hljs-number">235269</span>, <span class="hljs-number">11490</span>, <span class="hljs-number">970</span>, <span class="hljs-number">29871</span>, <span class="hljs-number">235265</span>]]),
 <span class="hljs-string">&#x27;attention_mask&#x27;</span>: tensor([[<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">1</span>]])
}<!-- HTML_TAG_END --></pre></div> <p data-svelte-h="svelte-m21ffs">This guide covers loading, encoding, decoding, batch processing, and the available tokenizer backends.</p> <h2 class="relative group"><a id="load-a-tokenizer" 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="#load-a-tokenizer"><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>Load a tokenizer</span></h2> <p data-svelte-h="svelte-ke93oc">Load a tokenizer with the <a href="/docs/transformers/pr_26617/en/model_doc/auto#transformers.AutoTokenizer">AutoTokenizer</a> class or a model-specific tokenizer class.</p> <div class="flex space-x-2 items-center my-1.5 mr-8 h-7 !pl-0 -mx-3 md:mx-0"><div class="flex items-center border rounded-lg px-1.5 py-1 leading-none select-none text-smd border-gray-800 bg-black dark:bg-gray-700 text-white">AutoTokenizer </div><div class="flex items-center border rounded-lg px-1.5 py-1 leading-none select-none text-smd text-gray-500 cursor-pointer opacity-90 hover:text-gray-700 dark:hover:text-gray-200 hover:shadow-sm">model-specific tokenizer </div></div> <div class="language-select"><p data-svelte-h="svelte-19q568c"><a href="/docs/transformers/pr_26617/en/model_doc/auto#transformers.AutoTokenizer.from_pretrained">AutoTokenizer.from_pretrained()</a> reads the model config, resolves the correct tokenizer class, and returns an instance of it. You don’t need to know the tokenizer class beforehand. Most tokenizers resolve to a subclass of <a href="/docs/transformers/pr_26617/en/main_classes/tokenizer#transformers.TokenizersBackend">TokenizersBackend</a>, a fast Rust-based tokenizer from the <a href="https://huggingface.co/docs/tokenizers/index" rel="nofollow">Tokenizers</a> library.</p> <p data-svelte-h="svelte-arjqni">Loading with <a href="/docs/transformers/pr_26617/en/model_doc/auto#transformers.AutoTokenizer">AutoTokenizer</a> is the recommended approach.</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 class=""><!-- 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;google/gemma-2-2b&quot;</span>)<!-- HTML_TAG_END --></pre></div> </div> <h2 class="relative group"><a id="encode-and-decode" 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="#encode-and-decode"><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>Encode and decode</span></h2> <p data-svelte-h="svelte-ek9spo">The <a href="/docs/transformers/pr_26617/en/internal/tokenization_utils#transformers.PreTrainedTokenizerBase.__call__">TokenizersBackend.<strong>call</strong>()</a> method encodes text or a batch of text into <code>input_ids</code>, <code>attention_mask</code>, and other model inputs. It also controls padding, truncation, and special token insertion.</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 class=""><!-- 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;google/gemma-2-2b&quot;</span>)
tokenizer(<span class="hljs-string">&quot;Sphinx of black quartz, judge my vow.&quot;</span>, return_tensors=<span class="hljs-string">&quot;pt&quot;</span>)
{
 <span class="hljs-string">&#x27;input_ids&#x27;</span>: tensor([[ <span class="hljs-number">2</span>, <span class="hljs-number">235277</span>, <span class="hljs-number">82913</span>, <span class="hljs-number">576</span>, <span class="hljs-number">2656</span>, <span class="hljs-number">30407</span>, <span class="hljs-number">235269</span>, <span class="hljs-number">11490</span>, <span class="hljs-number">970</span>, <span class="hljs-number">29871</span>, <span class="hljs-number">235265</span>]]),
 <span class="hljs-string">&#x27;attention_mask&#x27;</span>: tensor([[<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">1</span>]])
}<!-- HTML_TAG_END --></pre></div> <p data-svelte-h="svelte-1fqbhb2"><a href="/docs/transformers/pr_26617/en/internal/tokenization_utils#transformers.PreTrainedTokenizerBase.encode">TokenizersBackend.encode()</a> is similar but only returns the <code>input_ids</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> Copied</div></button></div> <pre class=""><!-- 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;google/gemma-2-2b&quot;</span>)
tokenizer.encode(<span class="hljs-string">&quot;Sphinx of black quartz, judge my vow.&quot;</span>)
[<span class="hljs-number">2</span>, <span class="hljs-number">235277</span>, <span class="hljs-number">82913</span>, <span class="hljs-number">576</span>, <span class="hljs-number">2656</span>, <span class="hljs-number">30407</span>, <span class="hljs-number">235269</span>, <span class="hljs-number">11490</span>, <span class="hljs-number">970</span>, <span class="hljs-number">29871</span>, <span class="hljs-number">235265</span>]<!-- HTML_TAG_END --></pre></div> <p data-svelte-h="svelte-1bsoml2"><a href="/docs/transformers/pr_26617/en/internal/tokenization_utils#transformers.PreTrainedTokenizerBase.decode">TokenizersBackend.decode()</a> converts a single sequence or batch of tokenized <code>input_ids</code> back to text.</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 class=""><!-- HTML_TAG_START -->tokenizer.decode(outputs[<span class="hljs-string">&quot;input_ids&quot;</span>])
[<span class="hljs-string">&#x27;&lt;bos&gt;Sphinx of black quartz, judge my vow.&#x27;</span>]<!-- HTML_TAG_END --></pre></div> <p data-svelte-h="svelte-1atfrau"><a href="/docs/transformers/pr_26617/en/internal/tokenization_utils#transformers.PreTrainedTokenizerBase.decode">TokenizersBackend.decode()</a> preserves the exact tokenization spacing. Set <code>clean_up_tokenization_spaces</code> to remove spaces before punctuation, and <code>skip_special_tokens</code> to strip special tokens from the output.</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 class=""><!-- HTML_TAG_START -->tokenizer.decode(outputs[<span class="hljs-string">&quot;input_ids&quot;</span>], skip_special_tokens=<span class="hljs-literal">True</span>)
[<span class="hljs-string">&#x27;Sphinx of black quartz, judge my vow.&#x27;</span>]<!-- HTML_TAG_END --></pre></div> <h2 class="relative group"><a id="special-tokens" 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="#special-tokens"><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>Special tokens</span></h2> <p data-svelte-h="svelte-owpjlb">Special tokens mark structural boundaries in a sequence, like the beginning-of-sequence or padding positions. Each model defines its own set of special tokens. The tokenizer adds them when you call it.</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 class=""><!-- HTML_TAG_START -->tokenizer.encode(<span class="hljs-string">&quot;Sphinx of black quartz, judge my vow.&quot;</span>)
[<span class="hljs-number">2</span>, <span class="hljs-number">235277</span>, <span class="hljs-number">82913</span>, <span class="hljs-number">576</span>, <span class="hljs-number">2656</span>, <span class="hljs-number">30407</span>, <span class="hljs-number">235269</span>, <span class="hljs-number">11490</span>, <span class="hljs-number">970</span>, <span class="hljs-number">29871</span>, <span class="hljs-number">235265</span>]
tokenizer.decode(outputs[<span class="hljs-string">&quot;input_ids&quot;</span>])
[<span class="hljs-string">&#x27;&lt;bos&gt;Sphinx of black quartz, judge my vow.&#x27;</span>]<!-- HTML_TAG_END --></pre></div> <p data-svelte-h="svelte-1l2gsfq">Register additional named special tokens with the <code>extra_special_tokens</code> argument. Multimodal models use them as placeholders for images, video, or audio.</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 class=""><!-- 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;google/gemma-3-4b-pt&quot;</span>,
 extra_special_tokens={<span class="hljs-string">&quot;image_token&quot;</span>: <span class="hljs-string">&quot;&lt;image&gt;&quot;</span>}
)<!-- HTML_TAG_END --></pre></div> <h2 class="relative group"><a id="batch-processing" 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="#batch-processing"><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>Batch processing</span></h2> <p data-svelte-h="svelte-1cshkxz">Batch processing tokenizes multiple sequences in a single call. <a href="/docs/transformers/pr_26617/en/main_classes/tokenizer#transformers.TokenizersBackend">TokenizersBackend</a> handles large batches faster because its Rust-based backend parallelizes work across threads.</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 class=""><!-- 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;google/gemma-2-2b&quot;</span>)
tokenizer(
 [
 <span class="hljs-string">&quot;Sphinx of black quartz, judge my vow.&quot;</span>,
 <span class="hljs-string">&quot;Pack my box with five dozen liquor jugs.&quot;</span>,
 <span class="hljs-string">&quot;How vexingly quick daft zebras jump!&quot;</span>
 ],
 return_tensors=<span class="hljs-string">&quot;pt&quot;</span>
)<!-- HTML_TAG_END --></pre></div> <p data-svelte-h="svelte-15vs1bl">Batch processing requires all sequences to share the same length. Padding and truncation are strategies to handle varying-length sequences.</p> <h3 class="relative group"><a id="padding" 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="#padding"><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>Padding</span></h3> <p data-svelte-h="svelte-1mmj2ia">Padding appends special tokens so shorter sequences match the longest sequence in a batch. The attention mask marks padding positions as <code>0</code> so the model ignores them. Set <code>padding=True</code> to pad to the longest sequence or pass <code>max_length</code> to pad to a fixed size.</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 class=""><!-- 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;google/gemma-2-2b&quot;</span>)
tokenizer(
 [
 <span class="hljs-string">&quot;Sphinx of black quartz, judge my vow.&quot;</span>,
 <span class="hljs-string">&quot;Pack my box with five dozen liquor jugs.&quot;</span>,
 <span class="hljs-string">&quot;How vexingly quick daft zebras jump!&quot;</span>
 ],
 return_tensors=<span class="hljs-string">&quot;pt&quot;</span>,
 padding=<span class="hljs-literal">True</span>,
)
{
 <span class="hljs-string">&#x27;input_ids&#x27;</span>: tensor([
 [ <span class="hljs-number">2</span>, <span class="hljs-number">235277</span>, <span class="hljs-number">82913</span>, <span class="hljs-number">576</span>, <span class="hljs-number">2656</span>, <span class="hljs-number">30407</span>, <span class="hljs-number">235269</span>, <span class="hljs-number">11490</span>, <span class="hljs-number">970</span>, <span class="hljs-number">29871</span>, <span class="hljs-number">235265</span>],
 [ <span class="hljs-number">0</span>, <span class="hljs-number">2</span>, <span class="hljs-number">6519</span>, <span class="hljs-number">970</span>, <span class="hljs-number">3741</span>, <span class="hljs-number">675</span>, <span class="hljs-number">4105</span>, <span class="hljs-number">25955</span>, <span class="hljs-number">42184</span>, <span class="hljs-number">225789</span>, <span class="hljs-number">235265</span>],
 [ <span class="hljs-number">0</span>, <span class="hljs-number">2</span>, <span class="hljs-number">2299</span>, <span class="hljs-number">73378</span>, <span class="hljs-number">17844</span>, <span class="hljs-number">4320</span>, <span class="hljs-number">224463</span>, <span class="hljs-number">4949</span>, <span class="hljs-number">48977</span>, <span class="hljs-number">9902</span>, <span class="hljs-number">235341</span>]
 ]),
 <span class="hljs-string">&#x27;attention_mask&#x27;</span>: tensor([
 [<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">1</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">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>]
 ])
}<!-- HTML_TAG_END --></pre></div> <blockquote class="note" data-svelte-h="svelte-1dbjo9j"><p>Large language models pad on the <em>left</em> side to avoid disrupting generation, which predicts the next token from the <em>right</em> side.</p></blockquote> <h3 class="relative group"><a id="truncation" 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="#truncation"><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>Truncation</span></h3> <p data-svelte-h="svelte-1ft2uza">Truncation clips tokens so a sequence fits within a maximum length. Set <code>truncation=True</code> and specify <code>max_length</code> to enable it.</p> <p data-svelte-h="svelte-1nuqojs">Padding and truncation work together. Short sequences gain padding tokens while long sequences lose trailing tokens. Together, they produce a packed rectangular tensor.</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 class=""><!-- 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;google/gemma-2-2b&quot;</span>)
tokenizer(
 [
 <span class="hljs-string">&quot;Sphinx of black quartz, judge my vow.&quot;</span>,
 <span class="hljs-string">&quot;Pack my box with five dozen liquor jugs.&quot;</span>,
 <span class="hljs-string">&quot;How vexingly quick daft zebras jump!&quot;</span>
 ],
 return_tensors=<span class="hljs-string">&quot;pt&quot;</span>,
 padding=<span class="hljs-literal">True</span>,
 truncation=<span class="hljs-literal">True</span>,
 max_length=<span class="hljs-number">5</span>
)
{
 <span class="hljs-string">&#x27;input_ids&#x27;</span>: tensor([
 [ <span class="hljs-number">2</span>, <span class="hljs-number">235277</span>, <span class="hljs-number">82913</span>, <span class="hljs-number">576</span>, <span class="hljs-number">2656</span>],
 [ <span class="hljs-number">2</span>, <span class="hljs-number">6519</span>, <span class="hljs-number">970</span>, <span class="hljs-number">3741</span>, <span class="hljs-number">675</span>],
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}<!-- HTML_TAG_END --></pre></div> <h2 class="relative group"><a id="backends" 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="#backends"><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>Backends</span></h2> <p data-svelte-h="svelte-1km33xh">Each model tokenizer is defined in a single file and supports four tokenization backends.</p> <table data-svelte-h="svelte-q7zkis"><thead><tr><th>backend</th> <th>implementation</th> <th>description</th></tr></thead> <tbody><tr><td><a href="/docs/transformers/pr_26617/en/main_classes/tokenizer#transformers.TokenizersBackend">TokenizersBackend</a></td> <td><a href="https://huggingface.co/docs/tokenizers" rel="nofollow">Tokenizers</a></td> <td>default for most models</td></tr> <tr><td><a href="/docs/transformers/pr_26617/en/main_classes/tokenizer#transformers.SentencePieceBackend">SentencePieceBackend</a></td> <td><a href="https://github.com/google/sentencepiece" rel="nofollow">SentencePiece</a></td> <td>models requiring SentencePiece</td></tr> <tr><td><a href="/docs/transformers/pr_26617/en/main_classes/tokenizer#transformers.PythonBackend">PythonBackend</a></td> <td>Python</td> <td>models requiring specialized custom tokenizers</td></tr> <tr><td><a href="/docs/transformers/pr_26617/en/model_doc/mixtral#transformers.MistralCommonBackend">MistralCommonBackend</a></td> <td><a href="https://mistralai.github.io/mistral-common/" rel="nofollow">mistral-common</a></td> <td>Mistral and Pixtral models</td></tr></tbody></table> <p data-svelte-h="svelte-6u5vzs">All backends inherit from <a href="/docs/transformers/pr_26617/en/internal/tokenization_utils#transformers.PreTrainedTokenizerBase">PreTrainedTokenizerBase</a> and share the same APIs for encoding, decoding, padding, truncation, saving, and loading. The difference is which tokenization pipeline runs underneath.</p> <p data-svelte-h="svelte-1snn7h7"><a href="/docs/transformers/pr_26617/en/model_doc/auto#transformers.AutoTokenizer">AutoTokenizer</a> selects the best available backend when you call <a href="/docs/transformers/pr_26617/en/model_doc/auto#transformers.AutoTokenizer.from_pretrained">from_pretrained()</a>.</p> <ol><li data-svelte-h="svelte-199ri7u"><p>It reads the <code>tokenizer_config.json</code> file for the <code>tokenizer_class</code> field.</p></li> <li><p data-svelte-h="svelte-fz0heg">The registry matches <code>tokenizer_class</code> to a class name. The resolved class inherits from one of the four backends. For example, <a href="/docs/transformers/pr_26617/en/model_doc/gemma#transformers.GemmaTokenizer">GemmaTokenizer</a> inherits from <a href="/docs/transformers/pr_26617/en/main_classes/tokenizer#transformers.TokenizersBackend">TokenizersBackend</a>, and <a href="/docs/transformers/pr_26617/en/model_doc/siglip#transformers.SiglipTokenizer">SiglipTokenizer</a> inherits from <a href="/docs/transformers/pr_26617/en/main_classes/tokenizer#transformers.SentencePieceBackend">SentencePieceBackend</a>.</p> <p data-svelte-h="svelte-1xkl0dk">Some models, like GLM, map directly to <a href="/docs/transformers/pr_26617/en/main_classes/tokenizer#transformers.TokenizersBackend">TokenizersBackend</a> because the <code>tokenizer.json</code> file fully describes the pipeline. <a href="/docs/transformers/pr_26617/en/model_doc/gemma#transformers.GemmaTokenizer">GemmaTokenizer</a> exists as a subclass since it defines additional model-specific settings in Python that <code>tokenizer.json</code> doesn’t capture.</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 class=""><!-- HTML_TAG_START -->TOKENIZER_MAPPING_NAMES = OrderedDict([
 (<span class="hljs-string">&quot;gemma2&quot;</span>, <span class="hljs-string">&quot;GemmaTokenizer&quot;</span> <span class="hljs-keyword">if</span> is_tokenizers_available() <span class="hljs-keyword">else</span> <span class="hljs-literal">None</span>),
 (<span class="hljs-string">&quot;glm&quot;</span>, <span class="hljs-string">&quot;TokenizersBackend&quot;</span> <span class="hljs-keyword">if</span> is_tokenizers_available() <span class="hljs-keyword">else</span> <span class="hljs-literal">None</span>),
 (
 <span class="hljs-string">&quot;mistral&quot;</span>,
 <span class="hljs-string">&quot;MistralCommonBackend&quot;</span>
 <span class="hljs-keyword">if</span> is_mistral_common_available()
 <span class="hljs-keyword">else</span> (<span class="hljs-string">&quot;TokenizersBackend&quot;</span> <span class="hljs-keyword">if</span> is_tokenizers_available() <span class="hljs-keyword">else</span> <span class="hljs-literal">None</span>),
 ),
 (<span class="hljs-string">&quot;siglip&quot;</span>, <span class="hljs-string">&quot;SiglipTokenizer&quot;</span> <span class="hljs-keyword">if</span> is_sentencepiece_available() <span class="hljs-keyword">else</span> <span class="hljs-literal">None</span>),
 ...
]<!-- HTML_TAG_END --></pre></div> <p data-svelte-h="svelte-1bd1sx1">When a backend like mistral-common isn’t installed, <a href="/docs/transformers/pr_26617/en/model_doc/auto#transformers.AutoTokenizer">AutoTokenizer</a> falls back to <a href="/docs/transformers/pr_26617/en/main_classes/tokenizer#transformers.TokenizersBackend">TokenizersBackend</a>.</p></li></ol> <p data-svelte-h="svelte-1fakyua">Check which backend a tokenizer is using with the <code>backend</code> property.</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 class=""><!-- 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;google/gemma-2-2b&quot;</span>)
tokenizer.backend
<span class="hljs-string">&#x27;tokenizers&#x27;</span><!-- HTML_TAG_END --></pre></div> <h2 class="relative group"><a id="inspect-the-tokenizer-architecture" 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="#inspect-the-tokenizer-architecture"><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>Inspect the tokenizer architecture</span></h2> <p data-svelte-h="svelte-1n8qt5">Inspect a tokenizer’s internal components (normalizer, pre-tokenizer, model, decoder) with the <code>_tokenizer</code> attribute.</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 class=""><!-- 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;google/gemma-2-2b&quot;</span>)
<span class="hljs-built_in">print</span>(tokenizer._tokenizer.normalizer)
<span class="hljs-built_in">print</span>(tokenizer._tokenizer.pre_tokenizer)
<span class="hljs-built_in">print</span>(tokenizer._tokenizer.model)
<span class="hljs-built_in">print</span>(tokenizer._tokenizer.decoder)<!-- HTML_TAG_END --></pre></div> <h2 class="relative group"><a id="resources" 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="#resources"><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>Resources</span></h2> <ul data-svelte-h="svelte-u99gy7"><li>The <a href="https://huggingface.co/blog/tokenizers" rel="nofollow">Tokenization in Transformers v5</a> post discusses the motivation behind the new tokenization backends.</li> <li>Review the <a href="https://github.com/huggingface/transformers/blob/main/MIGRATION_GUIDE_V5.md#tokenization" rel="nofollow">migration guide</a> for an overview of the tokenization changes.</li></ul> <a class="!text-gray-400 !no-underline text-sm flex items-center not-prose mt-4" href="https://github.com/huggingface/transformers/blob/main/docs/source/en/fast_tokenizers.md" target="_blank"><svg class="mr-1" 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="M31,16l-7,7l-1.41-1.41L28.17,16l-5.58-5.59L24,9l7,7z"></path><path d="M1,16l7-7l1.41,1.41L3.83,16l5.58,5.59L8,23l-7-7z"></path><path d="M12.419,25.484L17.639,6.552l1.932,0.518L14.351,26.002z"></path></svg> <span data-svelte-h="svelte-zjs2n5"><span class="underline">Update</span> on GitHub</span></a> <p></p>
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