[Python-Dev] the role of assert in the standard library ? (original) (raw)

Tarek Ziadé ziade.tarek at gmail.com
Thu Apr 28 14:09:17 CEST 2011

On Thu, Apr 28, 2011 at 12:27 PM, Michael Foord <fuzzyman at voidspace.org.uk> wrote:

On 28/04/2011 09:34, Terry Reedy wrote:

On 4/28/2011 3:54 AM, Tarek Ziadé wrote:

Hello I removed some assert calls in distutils some time ago because the package was not behaving correctly when people were using Python with the --optimize flag. In other words, assert became a full part of the code logic and removing them via -O was changing the behavior. In my opinion assert should be avoided completely anywhere else than in the tests. If this is a wrong statement, please let me know why :) My understanding is that assert can be used in production code but only to catch logic errors by testing supposed invariants or postconditions. It should not be used to test usage errors, including preconditions. In other words, assert presence or absence should not affect behavior unless the code has a bug. Agreed. We should ideally have buildbots doing test runs with -O and -OO. R. David Murray did a lot of work a year ago (or so) to ensure the test run passes with -OO but it easily degrades.. There are a couple of asserts in unittest (for test discovery) but I only use them to provide failure messages early. The functionality is unchanged (and tests still pass) with -OO. All the best,

I'll try to add a useful report on "bad asserts" in the bug tracker.

I am replying again to this on Python-ideas because I want to debate on assert :)

Cheers Tarek

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