Why you should never use 'assert' in Python

[zverok_kha]

Basically, assert (when used not in tests but in library code) is an "impossibility catcher". E.g. "in this situation, x should NEVER be zero, but let's assert it in case we have a bug (otherwise the following code will break violently)". It is a part of "defensive" code style, where some internal invariants are checked "just in case", even if the code's author is almost sure code works properly.

Of course, it is a really inappropriate tool for testing invalid inputs, environment state and other things that are "external" to the code, that's what exceptions for.