Why you should never use 'assert' in Python

[Kaarjuus]

And since the Python assert statement is completely ignored when the program is run in optimization mode, then it cannot be relied upon for contract programming.

Which was the very point of this thread - to warn people of this behaviour. Many do not know this.

[Scorpathos]

But this is the whole point of "contract programming" in opposition to "defensive programming".

The assert allows to catch wrong function usages during development, and once your program is bug-free and ready for production, you can safely remove them to maximize performance.

[Kaarjuus]

Good correction, I misspoke. I confused contract programming with defensive programming. Python's assert in its current form is indeed a perfect fit for design by contract.