Answer by John Mee for Best practice for using assert?

"assert" statements are removed when the compilation is optimized. So, yes, there are both performance and functional differences.

The current code generator emits no code for an assert statement when optimization is requested at compile time. - Python 2 DocsPython 3 Docs

If you use assert to implement application functionality, then optimize the deployment to production, you will be plagued by "but-it-works-in-dev" defects.

See PYTHONOPTIMIZE and -O -OO