[Python-Dev] PEP 572 and assert (original) (raw)

Chris Angelico rosuav at gmail.com
Tue Jul 17 04:56:36 EDT 2018

On Tue, Jul 17, 2018 at 6:50 PM, Serhiy Storchaka <storchaka at gmail.com> wrote:

Recently Barry shown an example:

assert len(subdirs := list(path.iterdir())) == 0, subdirs It looks awful to me. It looks even worse than using asserts for validating the user input. The assert has a side effect, and it depends on the interpreter option (-O). Even if subdirs is not used outside of the assert now, it is easy to introduce an error later, and it is hard to notice it if tests are not ran with the -O option regularly. Does PEP 572 encourages writing such code, discourages this, or completely forbids?

Asserts with side effects are already a bad idea. PEP 572 makes no change to this. If you're putting any sort of side effects inside assertions, you're playing with fire.

ChrisA

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