Language-Specific Review Notes

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

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.

== instead of === - always use strict equality.
async functions that are not awaited silently swallow errors.
Promise.all fails fast - unhandled rejections in parallel tasks crash the whole batch.
JSON.parse without try/catch throws on malformed input.
Mutating function parameters directly - causes hard-to-trace bugs.
Array.prototype.sort() without comparator sorts lexicographically, not numerically.
TypeScript: any types that could be unknown - forces callers to narrow before use.

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.
time.Sleep in tests - use channels or sync.WaitGroup instead.

.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.