The dangers of assert in Python

Python assert statements provide a concise way to verify assumptions during debugging and testing, raising an AssertionError with an optional message when a condition evaluates to false. A simple-interest example shows how asserts can identify invalid arguments such as non-positive integers, but it also demonstrates their central limitation: Python disables assertions when run in optimized mode with the -O flag, setting __debug__ to false and skipping all assert statements. Consequently, asserts should not be used for production input validation, normal error handling, control flow, authentication, or authorization, since disabled checks can lead to unexpected errors or serious security vulnerabilities, such as granting administrator access to users without an admin role. Safer alternatives for runtime validation include conditional statements, explicit exceptions, type hints, validators, unit tests, and debuggers, while asserts are best reserved for detecting programmer errors and isolating bugs during development.

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