Pycon Israel 2021

When is an exception not an exception? Using warnings in Python
2021-05-03, 10:00–10:25, General Track 1

Python's warnings are exceptions — but they're also distinct from exceptions, and are both used and trapped differently. In this talk, I'll introduce warnings, how to raise, trap, and redirect them, and show you best practices for their use.

If your code encounters a big problem, then you probably want to raise an exception. But what should your code do if it finds a small problem, one that shouldn't be ignored, but that doesn't merit an exception? Python's answer to this question is warnings.

In this talk, I'll introduce Python's warnings, close cousins to exceptions but still distinct from them. We'll see how you can generate warnings, and what happens when you do. But then we'll dig deeper, looking at how you can filter and redirect warnings, telling Python which types of warnings you want to see, and which you want to hide. We'll also see how you can get truly fancy, turning some warnings into (potentially fatal) exceptions and handling certain types with custom callback functions.

After this talk, you'll be able to take advantage of Python's warning system, letting your users know when something is wrong without having to choose between "print" and a full-blown exception.

Session language – English Target audience – Developers, Testers/QA, Integrators