[PyQt] Exceptions in Python Implementations of Virtuals

[Marcus Ottosson]

Imagine a case where a finance app developer misspells some attribute like
palette and has insufficient test coverage. Crashing the app in the middle
of trade execution is a much worse outcome than failing to color the line
edit correctly.

On the other hand, misspelling in this scenario could lead to the wrong
results not getting noticed until it’s much too late, in which case failing
fast costs less.

I don’t think there is any right or wrong answer here, I’d vouch for
sticking with what is the most Pythonic and leave C++ to C++.

Best,
Marcus
​

On 30 September 2014 17:52, Chris Colbert <sccolbert at gmail.com> wrote:

> I'm strongly -1 on this.
>
> I think exceptions should be handled consistently throughout the library.
> So if you were to make this change for virtual functions, it should also be
> made for signal handlers. But, user code excepting on the path of a signal
> handler or a virtual event method is very common in my experience, and not
> all of these exceptions prohibit the app from continuing to function.
>
> Fataling the app, on the other hand, would lead to absolute mayhem on the
> production floor.
>
> Imagine a case where a finance app developer misspells some attribute like
> palette and has insufficient test coverage. Crashing the app in the middle
> of trade execution is a much worse outcome than failing to color the line
> edit correctly.
>
> It would be nice to have an easier way than except hooks to be able to
> detect and handle these cases, and I think exploring options in that space
> is worthy of discussion. But I think qFatal is certainly the wrong approach
> here.
>  On Sep 30, 2014 12:24 PM, "Phil Thompson" <phil at riverbankcomputing.com>
> wrote:
>
>> Florian asked this question but it didn't result in any discussion, so
>> I'd like to have another poke at it.
>>
>> Currently, if an exception is raised by a Python re-implementation of a
>> C++ virtual then the exception is printed and the application continues. A
>> default result will be constructed by PyQt and returned to C++. Instead,
>> should PyQt print the exception and then terminate (by calling qFatal())?
>>
>> Some advantages...
>>
>> - consistency in what happens when an unhandled exception is raised (ie.
>> the application always terminates)
>> - such bugs become obvious and easy to find
>>
>> Some disadvantages...
>>
>> - incompatible with current behaviour
>> - may cause problems with applications that already try to handle such
>> exceptions using exception hooks
>>
>> If I make this change it will be for PyQt5 only. I don't plan to make the
>> change configurable in any way.
>>
>> Comments?
>>
>> Phil
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>
>
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-- 
*Marcus Ottosson*
konstruktion at gmail.com
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