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Exception Handling

Try-Except Blocks

Fundamental exception handling with try/except

Interview: Essential — tests understanding of Python error handling, exception hierarchy, and EAFP philosophy

Last Updated: June 12, 2026 • 7 min read

Exception handling with try/except is the foundation of robust Python programs. Python follows the EAFP (Easier to Ask Forgiveness than Permission) philosophy — try the operation and handle failures rather than checking conditions first. This leads to cleaner, more Pythonic code.

Exception Hierarchy

  • BaseException → root of all exceptions
  • Exception → all regular exceptions (catch this, not BaseException)
  • ValueError, TypeError, KeyError, IndexError → common built-in exceptions
  • SystemExit, KeyboardInterrupt → inherit from BaseException, not Exception

Best Practices

  • Catch specific exceptions, not bare except:
  • Use except Exception as e only as a last resort
  • Never catch BaseException (would catch Ctrl+C, SystemExit)
  • Keep try blocks small — only wrap the code that might raise

Interview Tip

Know the difference between EAFP (try/except) and LBYL (if/else checks). Python prefers EAFP because it avoids race conditions and is more readable.

Use Cases

Handling user input validation and parsing errors

File operations (missing files, permission errors)

Network requests (timeouts, connection failures)

API calls (JSON decode errors, missing keys)

Graceful degradation in production systems

Common Mistakes

Using bare except: — catches SystemExit, KeyboardInterrupt too

Catching Exception too broadly — hides bugs instead of fixing them

Making try blocks too large — only wrap code that might raise

Not logging exceptions — errors are silently swallowed

Catching BaseException — would prevent Ctrl+C from working