[Python-Dev] containment checking

[Glenn Linderman]

On 3/19/2010 3:02 PM, Antoine Pitrou wrote:
> Glenn Linderman<v+python<at>  g.nevcal.com>  writes:
>    
>> >  
>> >  Sounds to me like containment checking is wrong; that if it gets an
>> >  exception during the comparison that it should assume unequal, rather
>> >  than aborting, and continue to the next entry.
>>      
> Well as the Zen says:
>
> Errors should never pass silently.
> Unless explicitly silenced.
>
> If there's a bug in your __eq__ method, rather than getting wrong containment
> results, you get the proper exception.
>    

If there's a bug in your __eq__ method, it may or may not raise an 
exception, which may or may not get you wrong containment results.  But 
it will probably get you buggy results, somehow or another.  That's what 
design, code reviews, and testing are for.

If the your __eq__ method uses exceptions (the only available method of 
out-of-band signalling for binary operators; not all exceptions are 
errors) to declare that it can't perform the comparison and produce a 
boolean result, that is a case where producing an exception is not an 
error, so your quoted Zen doesn't apply.

Glenn