Editing Development/Python (section)

== Error handling ==

Errors are explicit. Never swallowed. Never hidden behind a generic fallback.

<syntaxhighlight lang="python">
# Wrong
try:
    result = parse_article(path)
except Exception:
    result = None

# Right
try:
    result = parse_article(path)
except FileNotFoundError:
    raise ArticleNotFoundError(article_id=article_id, path=path) from None
except etree.XMLSyntaxError as error:
    raise ArticleParseError(article_id=article_id, detail=str(error)) from error
</syntaxhighlight>

Custom exception classes inherit from a common base:

<syntaxhighlight lang="python">
class DuralexError(Exception):
    """Base exception for all Dura Lex errors."""

class ArticleNotFoundError(DuralexError):
    """Raised when a legislation article file does not exist on disk."""

class ArticleParseError(DuralexError):
    """Raised when a legislation article XML file cannot be parsed."""

class ReferenceResolutionError(DuralexError):
    """Raised when a legal reference is ambiguous or malformed."""
</syntaxhighlight>