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# Utilities for Tokenizers

This page lists all the utility functions used by the tokenizers, mainly the class
[`~tokenization_utils_base.PreTrainedTokenizerBase`] that implements the common methods between
[`PreTrainedTokenizer`] and [`PreTrainedTokenizerFast`] and the mixin
[`~tokenization_utils_base.SpecialTokensMixin`].

Most of those are only useful if you are studying the code of the tokenizers in the library.

## PreTrainedTokenizerBase

[[autodoc]] tokenization_utils_base.PreTrainedTokenizerBase
    - __call__
    - all

## SpecialTokensMixin

[[autodoc]] tokenization_utils_base.SpecialTokensMixin

## Enums and namedtuples

[[autodoc]] tokenization_utils_base.TruncationStrategy

[[autodoc]] tokenization_utils_base.CharSpan

[[autodoc]] tokenization_utils_base.TokenSpan