ROS2 Robust YAML Launch Parameter Validator

Problem Statement

Validate ROS2 launch configuration files before starting the robot. Misconfiguration is one of the most common causes of robot hardware damage — catching errors at config load time prevents crashes at runtime.

Requirements

Implement the function validate_launch_yaml(yaml_text, schema):

• Input: yaml_text (str) — raw YAML content; schema (dict) — validation rules
• Output: list of error strings — empty [] if valid, non-empty if invalid

Schema format

schema = {
    'launch': {'type': 'list', 'required': True},
    'version': {'type': 'float', 'required': False},
}

Validation rules your function must enforce

1. Parse the YAML safely (handle malformed YAML)
2. For each key in schema where required=True: fail if the key is missing
3. For each key that exists: fail if the value's type doesn't match type in schema
4. Return a descriptive error string for each violation

Example

validate_launch_yaml("launch: [1, 2]\nversion: 0.1", schema)
# Returns: []  ← valid

validate_launch_yaml("version: 0.1", schema)
# Returns: ["Missing required key: 'launch'"]  ← launch is missing

validate_launch_yaml("launch: \"not a list\"", schema)
# Returns: ["'launch' should be type list, got str"]  ← wrong type

⚠️ Common Pitfalls

• Using yaml.load() without Loader=yaml.SafeLoader — always use yaml.safe_load()
• Returning None instead of an empty list for valid YAML
• Not handling yaml.YAMLError for malformed input

📚 Helpful Resources

• PyYAML Documentation