What are acceptable use-cases for python's `assert` statement?
assert, python
Solution
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`.
Problem
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?