[Python-Dev] the role of assert in the standard library ?

[Barry Warsaw]

On Apr 28, 2011, at 04:34 AM, 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.

I would agree.  Use asserts for "this can't possibly happen <wink>"
conditions.

-Barry
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