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List:       pykde
Subject:    Re: [PyQt] How does sipParseArgs skip arguments?
From:       Shaheed Haque <srhaque () theiet ! org>
Date:       2017-04-17 22:45:48
Message-ID: CAHAc2jf50y4i-DWk2=H4Z8q27wPkOsYrszOw7TA1uyZkbH5ijg () mail ! gmail ! com
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Thanks, that makes sense.

On 17 April 2017 at 09:37, Phil Thompson <phil@riverbankcomputing.com> wrote:
> On 16 Apr 2017, at 12:55 pm, Shaheed Haque <srhaque@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
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