Language-Specific Review Notes

Reference this file during code review for language-specific pitfalls.

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Python

• Mutable default arguments: def f(x=[]) - the list is shared across all calls. Fix: def f(x=None): x = x or []
• Bare except: catches SystemExit and KeyboardInterrupt. Always use except Exception: at minimum.
• is vs == - is checks identity, not equality. Never use is to compare strings or integers outside of None checks.
• open() without with - file handles leak. Always use context manager.
• f-strings with side effects inside: f"{counter.increment()}" - avoid.
• threading.Thread without daemon=True blocks process exit.

JavaScript / TypeScript

• == instead of - always use strict equality.

Go

• Missing context.Context propagation in long-running operations - no cancellation support.
• defer inside a loop runs at function exit, not loop iteration - causes resource leaks.
• Ignoring the second return value of a map lookup: v := m[k] - v is zero value if missing.
• Goroutine leaks from channels that are never closed.

Rust

• .unwrap() in production code - should be ? or explicit error handling.
• .clone() used to satisfy the borrow checker instead of fixing the ownership model.
• unsafe blocks without a safety comment explaining the invariants.
• Integer overflow in debug mode panics, in release mode wraps - use checked arithmetic for untrusted input.

SQL

• String interpolation into queries - always use parameterised queries.
• SELECT * in production code - columns added later silently break assumptions.
• Missing index on foreign key columns used in JOINs.
• DELETE or UPDATE without WHERE clause.
• Transactions without explicit rollback on error.