Fix name_scope_stack AttributeError and IndexError in __exit__

[SamareshSingh]

• Add guard clauses to handle None and empty stack cases in name_scope.exit
• Prevents AttributeError when name_scope_stack is None (e.g., thread-local state cleared)
• Prevents IndexError when name_scope_stack is empty
• Add comprehensive tests for None stack, empty stack, multithreading scenarios
• Fixes [Bug] name_scope_stack causing exceptions #21831
• [Bug] name_scope_stack causing exceptions #21831

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[gemini-code-assist]

Summary of Changes

Hello @SamareshSingh, 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 significantly enhances the stability of the name_scope context manager by introducing defensive checks within its __exit__ method. These modifications prevent runtime errors that could arise from an uninitialized or empty name scope stack, particularly in complex or multithreaded execution flows. The changes are thoroughly validated with new, dedicated test cases, ensuring the name_scope functionality is more resilient and predictable across various operational conditions.

Highlights

• Robust Error Handling: Implemented guard clauses in the name_scope.__exit__ method to prevent AttributeError when name_scope_stack is None and IndexError when it is empty, addressing potential stability issues.
• Comprehensive Testing: Added extensive unit tests to cover scenarios where the name_scope_stack is None, empty, and to validate correct behavior in multithreaded environments, ensuring the fix is robust and thread-safe.
• Issue Resolution: Successfully fixes issue [Bug] name_scope_stack causing exceptions #21831, improving the reliability of the name_scope context manager.

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[gemini-code-assist]

Code Review

This pull request effectively addresses potential AttributeError and IndexError exceptions in name_scope.__exit__ by introducing necessary guard clauses. The new tests are thorough, covering the specific failure cases and multithreading scenarios to ensure robustness. My review includes a few suggestions to enhance code clarity and follow Pythonic conventions, particularly in the implementation of the fix and the structure of the new tests.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.66%. Comparing base (19ca9c1) to head (c1b8545).

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #21834   +/-   ##
=======================================
  Coverage   82.66%   82.66%           
=======================================
  Files         577      577           
  Lines       59477    59478    +1     
  Branches     9329     9330    +1     
=======================================
+ Hits        49167    49168    +1     
  Misses       7907     7907           
  Partials     2403     2403           

Flag	Coverage Δ
keras	82.48% <100.00%> (+<0.01%)	⬆️
keras-jax	63.31% <100.00%> (+<0.01%)	⬆️
keras-numpy	57.55% <100.00%> (+<0.01%)	⬆️
keras-openvino	34.34% <100.00%> (+<0.01%)	⬆️
keras-tensorflow	64.12% <100.00%> (+<0.01%)	⬆️
keras-torch	63.60% <100.00%> (+<0.01%)	⬆️

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