Home/ Questions/Q 568567
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-05-13T13:12:08+00:00

I often use python’s assert statement to check user input and fail-fast if we’re

  • 0

I often use python’s assert statement to check user input and fail-fast if we’re in a corrupt state. I’m aware that assert gets removed when python with the -o(optimized) flag. I personally don’t run any of my apps in optimized mode, but it feels like I should stay away from assert just in-case.

It feels much cleaner to write

assert filename.endswith('.jpg')

than

if not filename.endswith('.jpg'):
    raise RuntimeError

Is this a valid use case for assert? If not, what would a valid use-case for python’s assert statement be?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    Assertions should be used for expressing invariants, or preconditions.
    In your example, you are using them for checking unexpected input – and that’s a completely different class of exceptions.

    Depending on the requirements, it may be perfectly OK to raise an exception on wrong input, and stop the application; however the code should always be tailored for expressiveness, and raising an AssertionError is not that explicit.
    Much better would be to raise your own exception, or a ValueError.

    • 0