effective-error-handling.md

tier	technology
name	Effective Python Error Handling
description	Directives on using try/except/finally blocks correctly and creating custom exceptions.
tags	python error-handling exceptions best-practices
layer

Effective Python Error Handling

Primary Directive

You MUST use try/except/finally blocks to handle potential errors gracefully. Exceptions caught MUST be as specific as possible to avoid hiding bugs.

Process

1. Catch Specific Exceptions: Always catch the most specific exception possible (e.g., except ValueError:) rather than a bare except:. This prevents catching unexpected errors.
2. Use finally for Cleanup: Place code that MUST be executed regardless of whether an exception occurred (e.g., closing a file or a network connection) in a finally block.
3. Don't Suppress Exceptions: Do not use except: pass to silently ignore errors. If an exception is caught, it MUST be handled appropriately, logged, or explicitly re-raised.
4. Create Custom Exceptions: For application-specific error conditions, create custom exception classes by inheriting from Python's built-in Exception class. This makes error handling more explicit.
5. Keep try Blocks Small: The try block MUST contain only the specific line(s) of code that might raise the exception you are catching.

Constraints

• Do NOT catch broad exceptions like Exception or BaseException unless you are at the top level of your application and intend to log the error before exiting.
• Error messages in custom exceptions MUST be clear, informative, and describe the error condition precisely.
• Avoid using exceptions for normal control flow.