FIX: prevent AttributeError in __del__ on partially-initialized Cursor

[subrata-ms]

Work Item / Issue Reference

AB#45943

GitHub Issue: #642

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Summary

This pull request improves the robustness of the Cursor class initialization and cleanup logic, ensuring that partially-initialized or half-constructed cursor objects are handled safely and do not cause unraisable exceptions during garbage collection. It also adds regression tests to prevent recurrence of related bugs.

Initialization and cleanup robustness:

• The __init__ method in cursor.py now sets self.closed = False and self.hstmt = None as the very first statements, before any code that might raise an exception, ensuring that even partially-initialized Cursor instances have a consistent state for cleanup. [1] [2]
• The close() method now safely checks for the existence of the closed attribute using getattr(self, "closed", True), preventing AttributeError if the attribute is missing (e.g., in half-initialized objects).
• The __del__ method now uses the correct sys.is_finalizing() function (instead of the incorrect sys._is_finalizing()) and guards logging calls to prevent unraisable exceptions during interpreter shutdown.

Testing and regression prevention:

• Adds test_cursor_del_half_initialized_cursor_no_errors and test_cursor_init_failure_leaves_consistent_state to ensure that half-initialized cursors do not raise unraisable exceptions during garbage collection and that failed initialization leaves the cursor and connection in a consistent, recoverable state.

[Copilot]

Pull request overview

This PR hardens mssql_python.cursor.Cursor lifecycle behavior to avoid unraisable exceptions during garbage collection when a Cursor is only partially initialized, and adds regression tests to prevent recurrence of the CI PytestUnraisableExceptionWarning seen in issue #642.

Changes:

• Establishes Cursor cleanup invariants earlier in __init__ (closed=False, hstmt=None) so close()/__del__ can run safely even after initialization failures.
• Makes Cursor.close() tolerant of instances missing the closed attribute (e.g., objects created via Cursor.__new__).
• Fixes __del__ finalization check to use sys.is_finalizing() and guards debug logging during interpreter shutdown; adds lifecycle regression tests.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
mssql_python/cursor.py	Makes cursor initialization/cleanup resilient to partial construction and interpreter shutdown edge cases.
tests/test_005_connection_cursor_lifecycle.py	Adds regression tests for half-initialized cursor GC paths and failed cursor construction scenarios.

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[saurabh500]

@subrata-ms generally looks good to me. The copilot comment on the test is interesting.