🧩 Improved Error Message for Invalid `parameters.key`

Summary: Adds clarity for YAML debugging in Observation mode.

URL: https://gitlab.com/esa/pyxel/-/merge_requests/1093

Date: 2025-10-22

📖 Overview

This update improves how Pyxel handles invalid parameters.key values in the Observation mode. Previously, a vague KeyError made debugging difficult when a user referenced an incorrect key in the YAML configuration.

Project Details

Project: Pyxel – ESA GitLab
Branch: enhance-keyerror-observation
Area: pyxel/observation/observation.py
Type: Developer Experience / Error Handling
Merge Request: !1093

🧠 Change Summary

The validate_steps() method in the Observation class has been updated to:

Detect which part of the parameter key is invalid.
Visually highlight the incorrect segment with a caret (^).
Add a clear explanatory message, e.g. "Non-existing parameter".

💡 Example Before and After

Before:

KeyError: "Missing parameter: 'cfg.pipeline.charge_generation.exponential_qe.arguments.x_epi'"

After:

KeyError: "Missing parameter: 'cfg.pipeline.charge_generation.exponential_qe.arguments.x_epi'
                                                                            ^^^^^
                                                                            Non-existing parameter"

This new message clearly identifies the problematic part of the key, improving clarity and debugging speed for all users.

🧪 Testing

A dedicated test script run_observation_test.py was written to simulate invalid keys. It confirmed that the improved error message displays correctly and clearly.