Mario Corchero - How to properly raise, handle and create them.

Did you know there are multiple ways to raise and capture exceptions? Have you ever wondered if you should raise a built-in exception or create your own hierarchy? Did you ever find it hard to understand what an exception meant?

This talk will go through the decisions needed to raise and capture exceptions when creating a library. We will look at how to translate and handle errors, create your own exceptions, and make exceptions clear and easy to troubleshoot, while also understanding how they actually work, common pitfalls.

https://us.pycon.org/2019/schedule/presentation/225/

Transcript

1. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Exceptional Exceptions How to properly raise, handle and create them PyCon 2019 Mario Corchero @mariocj89
2. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Let’s just raise an exception, right?
3. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Let’s just raise an exception, right?
4. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Let’s just raise an exception, right?
5. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Let’s just raise an exception, right?
6. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Let’s just raise an exception, right?
7. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Let’s just raise an exception, right?
8. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Let’s go step by step
9. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. How to capture an exception
10. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. What can go in the except?
11. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. What can go in the except?
12. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Using finally
13. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Using else
14. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Order of execution?
15. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. What about returning in the middle?
16. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Logging exceptions Use exc_info to include exception information
17. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Logging exceptions
18. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Logging exceptions Errors should never pass silently. Unless explicitly silenced.
19. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Logging exceptions
20. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Logging exceptions
21. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Scoping of the except See PEP 3110. In short: exception -> traceback -> stack frame -> exception
22. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Raising exceptions
23. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Raising exceptions
24. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Raising exceptions
25. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Raise it!
26. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. The tricky raise within except
27. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. The tricky, raise within except
28. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Reraise
29. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Reraise
30. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Reraise
31. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Reraise
32. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Chaining exceptions
33. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Chaining exceptions
34. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Eliding previous exception
35. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Eliding previous exception
36. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. False friends: NotImplemented Passes without printing. 37,762 hits in GitHub as of Apr 2019.
37. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Raise on a thread?
38. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Raise on a thread?
39. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Creating exceptions
40. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Creating exceptions
41. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. The exception hierarchy Check https://docs.python.org/3/library/exceptions.html
42. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Exception attributes
43. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Exception attributes
44. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Exception attributes
45. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Creating new classes
46. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Creating new classes
47. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Exception hierarchy
48. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Multiple inheritance • Decimal: • Requests:
49. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Can I use Error codes?
50. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Conclusions
51. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Q&A Ask me about travelling to Extremadura!
52. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Bonus!
53. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Bonus!
54. © 2018 Bloomberg Finance L.P. All rights reserved. © 2019 Bloomberg Finance L.P. All rights reserved. Bonus!