[PyQt] How does sipParseArgs skip arguments?

[Shaheed Haque]

Thanks, that makes sense.

On 17 April 2017 at 09:37, Phil Thompson <phil at riverbankcomputing.com> wrote:
> On 16 Apr 2017, at 12:55 pm, Shaheed Haque <srhaque at theiet.org> wrote:
>>
>> When using %MethodCode, the SIP-generated part of the output generally
>> includes a call to sipParseArgs. Now, the documentation for
>> %MethodCode explains the use of sipArgs as a tuple, so it is clear
>> that handwritten code for argument N should extract the N'th entry in
>> sipArgs and proceed as required.
>
> No. You should always refer to the arguments as 'a0', 'a1' etc.
>
>> What I'd like to understand is how sipParseArgs knows to skip an
>> argument which is to be handled manually? For example (using SIP 4.18)
>> and these two similar functions:
>>
>>    KEmoticonsTheme newTheme(const QString &name, KService &service,
>> bool dummy);
>>    KEmoticonsTheme newTheme2(const QString &name, const
>> QExplicitlySharedDataPointer<KService> &service, bool dummy)
>>    [KEmoticonsTheme(const QString &name, const
>> QExplicitlySharedDataPointer<KService> &service, bool dummy)];
>> %MethodCode
>> // TBD
>> %End
>>
>> The first function gets its arguments like this:
>>
>> =====================
>>       const QString* a0;
>>        int a0State = 0;
>>        KService* a1;
>>        bool a2;
>>        KEmoticons *sipCpp;
>>
>>        if (sipParseArgs(&sipParseErr, sipArgs, "BJ1J9b", &sipSelf,
>> sipType_KEmoticons, &sipCpp, sipType_QString,&a0, &a0State,
>> sipType_KService, &a1, &a2))
>> =====================
>>
>> whereas the second version skips a1 like this:
>>
>> =====================
>>        const QString* a0;
>>        int a0State = 0;
>>        QExplicitlySharedDataPointer<KService> a1;
>>        bool a2;
>>        KEmoticons *sipCpp;
>>
>>        if (sipParseArgs(&sipParseErr, sipArgs, "BJ1b", &sipSelf,
>> sipType_KEmoticons, &sipCpp, sipType_QString,&a0, &a0State, &a2))
>> =====================
>>
>> I need to generate the code to extract a1 from sipArgs, but in
>> general, what are the rules that govern whether sipParseArgs will or
>> will not extract arguments? And in the second case, how does it know
>> to extract a0 and then a2, but not a1?
>
> I'm guessing that #2 is because you got an error message saying that you had to provide %MethodCode and a C++ signature. The reason is that SIP does not understand the signature as a Python signature. There is no point in providing explicit Python and C++ signatures if they are the same. You need to provide a Python signature that corresponds to what the Python programmer will be using (or provide a mapped type for the problematic argument). The purpose of the %MethodCode is to provide the bridge between the Python signature and the C++ signature.
>
> Yes - the error reporting could be improved.
>
> Phil