Python Error Handling Patterns

HARD violations (must fix)

Bare except

• Pattern: except: with no exception type.
• Example: except: catches KeyboardInterrupt, SystemExit, and every other exception.
• Why HARD: Catches everything including signals that should propagate. Always specify an exception type.

Empty except blocks

• Pattern: except SomeError: pass or except SomeError: ....
• Example: except ValueError: pass.
• Why HARD: Silently swallows the error. The caller has no way to know the operation failed.

Broad except Exception without re-raise

• Pattern: except Exception: (or except BaseException:) where the body does not re-raise.
• Example: except Exception: return None.
• Why HARD: Catches far too broadly and swallows the error. Either narrow the exception type or re-raise.
• Note: except Exception: return None also matches the SHOULD "silent fallback" rule below, but per the intra-rule precedence clause this location is reported only as HARD.

SHOULD violations (fix or justify)

Silent fallback returns

• Pattern: except SomeError: return None (or any default value) without logging.
• Note: if the except block logs before returning the default, this downgrades to WARN.
• Justification: acceptable in lookup-style functions where None is a documented "not found" return.

WARN (advisory)

Log-only handling

• Pattern: except SomeError as e: logger.error(e) with no raise, return, or other control flow.
• Why WARN: Logging is better than ignoring, but the caller still has no signal. May be intentional in background tasks.