fix(transformers): support loading weight from explicit transformers weights

[wcrzlh]

…weight

What does this PR do?

Fixes # (issue)

Adds # (feature)

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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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[gemini-code-assist]

Summary of Changes

Hello @wcrzlh, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request enhances the from_pretrained function in modeling_utils.py to support loading weights from explicitly specified Transformers weights files. It adds validation for the specified file type and adjusts the logic for local file handling to prioritize these explicit weights. This change allows users to load weights from .safetensors files directly, providing more flexibility in weight loading.

Highlights

• Weight Loading: This PR introduces support for loading weights from explicit Transformers weights files, specifically focusing on .safetensors and .safetensors.index.json formats.
• Configuration Validation: It adds a validation check to ensure that the transformers_weights configuration points to a valid .safetensors file or index file.
• Local File Handling: The changes modify the logic for handling local files, prioritizing the explicitly defined transformers_weights file when specified.
• Filename Handling: The PR updates the filename resolution logic to use the explicitly defined transformers_weights filename when available.

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[gemini-code-assist]

Code Review

This pull request adds support for loading model weights from an explicit filename specified in the configuration, which is a useful feature. The implementation correctly prioritizes this explicit filename when loading weights for both local and remote models. My review includes a suggestion to improve code conciseness and points out a small code duplication that could be refactored for better maintainability.

[gemini-code-assist]

The endswith method can accept a tuple of strings to check against. Using it will make the condition more concise and readable.

            if not transformers_explicit_filename.endswith((".safetensors", ".safetensors.index.json")):

[gemini-code-assist]

This logic to determine is_sharded is duplicated on line 2580. To improve maintainability and avoid repetition, consider determining this value once, right after transformers_explicit_filename is retrieved from the config.