# Error Handling

> Error handling guidelines for NeMo-RL. Covers exception specificity, minimal try bodies, and else blocks.

- Skill: `nvidia-nemo-rl/error-handling` (Agent Skill)
- Install (CLI): `npx skillmds@latest add nvidia-nemo-rl/error-handling`
- Raw SKILL.md: https://api.skillmd.com/api/skills/nvidia-nemo-rl/error-handling/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: AI & ML
- Author: NVIDIA-NeMo (https://skillmd.com/u/nvidia-nemo-rl)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/nvidia-nemo-rl/error-handling

---


# Error Handling

## Use Specific Exceptions

When using try-except blocks, limit the except to the smallest set of errors possible.

**Don't:**
```python
try:
    open(path, "r").read()
except:
    print("Failed to open file")
```

**Do:**
```python
try:
    open(path, "r").read()
except FileNotFoundError:
    print("Failed to open file")
```

## Fail Loud, Not Silent

When adding a config option or branch, ask: what does the worst plausible misconfiguration do? If it silently
produces *wrong results* rather than an error, add a setup-time `assert`/`raise` so it fails loudly at startup
instead of corrupting a run.

**Examples of silent-wrong worth guarding:**
- An advantage estimator that needs a real `prev_logprobs` while a loss flag zeroes it (advantage degrades to
  garbage with no error).
- An agent routed to a teacher alias that has no worker group (cryptic `KeyError` mid-run instead of a
  setup-time check).
- A backend/quantization setting silently ignored for a sub-component.

Prefer failing at `setup()` time over a deep-in-the-loop crash; prefer a crash over silent garbage. If you
truly can't validate, surface a logged warning rather than nothing.