# Debug leftovers: `debugger`, `breakpoint()`, `print("here")`, `print(f"{x=}")`, `dbg!`

*Code nobody needs*: one of the ways AI coding agents bloat software, from lessloc's [pattern catalog](https://lessloc.org/patterns/index.md). lessloc catches it as [`debug-leftover`](https://lessloc.org/guide/reference.md#tier-1).

## What makes debug leftovers a bad practice?

The standards that call it a bad practice: [CWE-489](https://cwe.mitre.org/data/definitions/489.html) Active Debug Code; ESLint no-debugger; Sonar S4507; clippy dbg_macro.

## What does lessloc do about debug leftovers?

lessloc catches it as [`debug-leftover`](https://lessloc.org/guide/reference.md#tier-1). It is judged at turn end, because mid-work the print may still be in use.

- `debug-leftover` (tier 1): `debugger`, `breakpoint()`, `pdb.set_trace()`, or a debug print such as `print("here")`. Judged when the turn ends.

## Examples

Caught as `debug-leftover`:

```js [e.js]
export function total(xs) {
  debugger;
  console.log("here");
  return xs.length;
}
```

Written well:

```js [e.js]
export function total(xs) {
  console.log(`total of ${xs.length} items`);
  return xs.length;
}
```

Caught as `debug-leftover`:

```python [f.py]
def total(xs):
    breakpoint()
    print(f"{xs=}")
    return len(xs)
```

Written well:

```python [f.py]
def total(xs):
    print(f"{len(xs)} items")
    return len(xs)
```

## Related patterns

The other patterns in [Code nobody needs](https://lessloc.org/patterns/index.md#code-nobody-needs):

- [Options, flags, parameters or config for needs nobody named](https://lessloc.org/patterns/speculative-options.md): lessloc gives every session a rule against it and catches it as `mode-flag`.
- [An interface or abstract class with one implementation](https://lessloc.org/patterns/single-impl.md): lessloc catches it as `single-impl`.
- [Wrappers that only forward; barrel files that only re-export](https://lessloc.org/patterns/wrappers.md): lessloc catches it as `wrapper`.
- [A new function or import that nothing calls or tests](https://lessloc.org/patterns/unused.md): lessloc catches it as `unused` (ruff adds unused variables).
- [Obsolete code kept behind a guard or flag instead of deleted](https://lessloc.org/patterns/guarded-dead-code.md): lessloc gives every session the rule: delete what the change makes dead.
- [Tombstones](https://lessloc.org/patterns/tombstones.md): lessloc catches it as `history`.
- [Stubs and fake success](https://lessloc.org/patterns/stubs.md): lessloc catches it as `stub`; it asks to finish the code or to tell the user what is not real yet.
- [Placeholders: # ... existing code ..., "your code here"](https://lessloc.org/patterns/placeholders.md): lessloc catches it as `placeholder` and refuses it before it lands.
- [Commented-out code](https://lessloc.org/patterns/commented-out.md): lessloc catches it as `commented-out` and refuses it before it lands.
- [A demo \_\_main\_\_ block or demo folder nobody asked for](https://lessloc.org/patterns/demo-code.md): lessloc catches it as `demo-code` and `new-folder`.
- [Hand-written boilerplate a language feature writes](https://lessloc.org/patterns/boilerplate.md): lessloc catches it as `simpler`.
- [A one-line helper used once](https://lessloc.org/patterns/single-use.md): lessloc catches it as `single-use`.
- [TODO and FIXME left behind](https://lessloc.org/patterns/todo.md): lessloc catches it as `todo`; it asks to finish the work, or to record known debt as `shortcut:` and tell the user.