Repository: huggingface/transformers
Pull request: Explicitly setting encoding in tokenization_utils_base.py

Add encoding explicitly

# What does this PR do?

**Problem**:

When loading tokenizers, specifically those that utilize a chat_template.jinja file (e.g., THUDM/GLM-4-9B-0414), a UnicodeDecodeError can occur in certain environments. This happens because the open() call defaults to the system's preferred encoding, which can unexpectedly revert to ASCII (ANSI_X3.4-1968) within subprocesses, particularly in torch.distributed settings or isolated container environments.

The root cause is that these subprocesses may not correctly inherit LANG, LC_ALL, or LC_CTYPE environment variables from the parent shell, leading locale.getpreferredencoding() to return ASCII instead of UTF-8. This results in the following traceback when encountering non-ASCII bytes (e.g., 0xe5) in the chat_template.jinja file:
```
chat_template_handle <_io.TextIOWrapper name='/root/.cache/huggingface/hub/models--THUDM--GLM-4-9B-0414/snapshots/645b8482494e31b6b752272bf7f7f273ef0f3caf/chat_template.jinja' mode='r' encoding='ANSI_X3.4-1968'>
chat_template_handle.read()
Traceback (most recent call last):
  File "<string>", line 1, in <module>
  File "/root/.local/share/uv/python/cpython-3.12.9-linux-x86_64-gnu/lib/python3.12/encodings/ascii.py", line 26, in decode
    return codecs.ascii_decode(input, self.errors)[0]
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
UnicodeDecodeError: 'ascii' codec can't decode byte 0xe5 in position 43: ordinal not in range(128)
```
**Solution**:

This PR explicitly sets the encoding="utf-8" parameter when opening the file. It then works as expected.


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- [ ] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).
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      Pull Request section?
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      to it if that's the case.
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      [documentation guidelines](https://github.com/huggingface/transformers/tree/main/docs), and
      [here are tips on formatting docstrings](https://github.com/huggingface/transformers/tree/main/docs#writing-source-documentation).
- [ ] Did you write any new necessary tests?


## Who can review?

Anyone in the community is free to review the PR once the tests have passed. Feel free to tag
members/contributors who may be interested in your PR.

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 If you know how to use git blame, that is the easiest way, otherwise, here is a rough guide of **who to tag**.
 Please tag fewer than 3 people.

Models:

- text models: @ArthurZucker
- vision models: @amyeroberts, @qubvel
- speech models: @eustlb
- graph models: @clefourrier

Library:

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- generate: @zucchini-nlp (visual-language models) or @gante (all others)
- pipelines: @Rocketknight1
- tensorflow: @gante and @Rocketknight1
- tokenizers: @ArthurZucker
- trainer: @zach-huggingface and @SunMarc
- chat templates: @Rocketknight1

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- rust tokenizers: [different repo](https://github.com/huggingface/tokenizers)

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Changed files:
filename: src/transformers/tokenization_utils_base.py
patch: @@ -2086,7 +2086,7 @@ def _from_pretrained(
         chat_template_file = resolved_vocab_files.pop("chat_template_file", None)
         extra_chat_templates = [key for key in resolved_vocab_files if key.startswith("chat_template_")]
         if chat_template_file is not None:
-            with open(chat_template_file) as chat_template_handle:
+            with open(chat_template_file, encoding="utf-8") as chat_template_handle:
                 chat_templates["default"] = chat_template_handle.read()
         for extra_chat_template in extra_chat_templates:
             template_file = resolved_vocab_files.pop(extra_chat_template, None)