perf: replace KeyError exception with dict.get() in BoundStatement.bi…

[mykaul]

…nd()

Replace try/except KeyError with dict.get() + sentinel pattern in the per-column binding loop of BoundStatement.bind(). This loop runs once per column per execute() call for dict-style bindings, making it a hot path. Using dict.get() avoids the overhead of raising and catching KeyError for every missing/optional column.

The sentinel object (_BIND_SENTINEL) is necessary to distinguish a missing key from an explicit None value in the bound dict.

Pre-review checklist

• I have split my patch into logically separate commits.
• All commit messages clearly explain what they change and why.
• I added relevant tests for new features and bug fixes.
• All commits compile, pass static checks and pass test.
• PR description sums up the changes and reasons why they should be introduced.
• I have provided docstrings for the public items that I want to introduce.
• I have adjusted the documentation in ./docs/source/.
• I added appropriate Fixes: annotations to PR description.

[Copilot]

Pull request overview

Improves the performance of dict-style parameter binding in BoundStatement.bind() by avoiding KeyError exception handling in the per-column binding loop, which is on a hot path during execute() for prepared statements.

Changes:

• Introduces a private sentinel (_BIND_SENTINEL) to distinguish “missing key” from an explicit None.
• Replaces try/except KeyError with dict.get(..., sentinel) in the dict-binding loop to avoid exception overhead.

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.

[mykaul]

Review of Copilot's Comments

Comment 1: Module-level _BIND_SENTINEL exposure

Copilot's concern: The sentinel could be accidentally used by callers.

Assessment: Low severity, mostly noise. The _ prefix is the standard Python convention for private objects. Moving it inside bind() would create a new object() on every call to a hot path — counterproductive for a performance PR. The suggestion to use UNSET_VALUE instead would complicate the logic with separate v3/v4 code paths for marginal benefit.

Comment 2: dict.get() doesn't call __missing__

Copilot's concern: Switching from values_dict[col.name] (which triggers __missing__ for subclasses like defaultdict) to values_dict.get() is a behavior change.

Assessment: Technically correct, but negligible practical impact. Using a defaultdict for binding parameters would be unusual and arguably a misuse — it would silently provide defaults for missing columns instead of raising errors. No evidence in the codebase or tests that __missing__-implementing subclasses are used here.

Additional Observations

1. The optimization is sound — avoiding try/except KeyError on a hot path is a reasonable micro-optimization.
2. No bugs introduced — the new logic correctly handles all three cases (key present, key missing on v4+, key missing on v3). Existing unit tests cover these paths.
3. _BIND_SENTINEL export is a non-issue — no __all__ in the module, and the _ prefix excludes it from wildcard imports.
4. Missing benchmark data — the PR would be strengthened by including before/after timings, though this isn't blocking.