Add fallback for environments where ctypes.PythonAPI is not available.

[googlyrahman]

The newly introduced prefetcher and buffer components utilize the ctypes library, specifically relying on the CPython C-API (ctypes.pythonapi) for optimized, gil-free, zero-copy memory operations. While ctypes is available in alternative Python implementations like PyPy, the ctypes.pythonapi module is not supported in those environments.

To address this, this PR introduces a graceful fallback mechanism. If an exception occurs while attempting to load ctypes.pythonapi, the code now safely falls back to native Python slicing and standard bytearray allocations. This ensures full cross-platform compatibility for the prefetcher and buffer across different Python implementations, trading a minor performance hit for broader support.

More about this discussion can be found here: #888 (comment)

[gemini-code-assist]

Code Review

This pull request introduces fallback mechanisms for environments without CPython-specific ctypes APIs (such as PyPy) in both gcsfs/prefetcher.py and gcsfs/zb_hns_utils.py. When these APIs are unavailable, the code now gracefully falls back to standard Python slicing and bytearray operations. Corresponding unit tests have also been added to verify these fallback paths. The review feedback suggests explicitly defining the CPython-specific ctypes API variables as None in the fallback except blocks to prevent static analysis or linter warnings about undefined names. Additionally, it is recommended to refactor the defensive check in DirectMemmoveBuffer to avoid using a dummy value of -1 for _start_address when falling back to bytearray.

[codecov]

Codecov Report

❌ Patch coverage is 88.23529% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.68%. Comparing base (3bd3383) to head (ef99268).

Files with missing lines	Patch %	Lines
gcsfs/zb_hns_utils.py	84.61%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #938      +/-   ##
==========================================
- Coverage   89.77%   89.68%   -0.09%     
==========================================
  Files          16       16              
  Lines        3569     3579      +10     
==========================================
+ Hits         3204     3210       +6     
- Misses        365      369       +4     

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[googlyrahman]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces safe fallbacks for non-CPython environments (such as PyPy) where CPython-specific ctypes APIs are unavailable. It wraps the loading of PyBytes_FromStringAndSize and PyBytes_AsString in try-except blocks across gcsfs/prefetcher.py and gcsfs/zb_hns_utils.py, falling back to standard Python slicing and bytearray operations when these APIs are missing. Additionally, unit tests are added to verify these fallback paths. The reviewer suggests importing the CPython API detection variables from gcsfs.prefetcher into gcsfs.zb_hns_utils.py to avoid code duplication.

[googlyrahman]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces fallback mechanisms for non-CPython environments (such as PyPy) where CPython-specific ctypes APIs are unavailable. It conditionally uses standard Python slicing and bytearray operations when HAS_CPYTHON_API is false, and adds corresponding unit tests to verify this fallback behavior. The reviewer suggests optimizing the non-CPython fallback path in DirectMemmoveBuffer by utilizing a memoryview over the bytearray to perform more efficient, in-place slice assignments.

[googlyrahman]

@zhixiangli, we can merge this.