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List:       pykde
Subject:    Re: [PyQt] pyqtSlot
From:       Phil Thompson <phil () riverbankcomputing ! com>
Date:       2016-08-25 16:10:50
Message-ID: EEDA265A-9E74-4D4A-8D21-3AF47735DFA7 () riverbankcomputing ! com
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On 25 Aug 2016, at 5:00 pm, oliver <oliver.schoenborn@gmail.com> wrote:
> 
> 
> On Thu, Aug 25, 2016 at 11:25 AM, Phil Thompson <phil@riverbankcomputing.com> wrote:
> On 25 Aug 2016, at 2:24 pm, oliver <oliver.schoenborn@gmail.com> wrote:
> > 
> > 
> > 
> > On Thu, Aug 25, 2016 at 8:40 AM, Phil Thompson <phil@riverbankcomputing.com> wrote:
> > 
> > Inspect the QMetaObject to see if the slot is there as you would expect.
> > 
> > > 
> > > If the slot weren't in the QMetaObject, how would the object method
> > > get called (it does get called)?
> > 
> > The same way any other type of callable is handled, by creating a proxy QObject when the \
> > connection is made. 
> > 
> > The slot will surely be in the wrapper's proxy QObject.QMetaObject
> 
> No it won't, that's not how the proxy works.
> 
> > but what's the concern with that? As long as the connection is established from the correct \
> > thread, the proxy QObject will be owned by the correct thread so the proxy slot will be \
> > called in the correct thread, and this in turn will call the slot_wrapper which will call \
> > our QObject's method. Should all be good, no?
> 
> But why bother with pyqtSlot at all if you don't care about it being in the QMetaObject?
> 
> Phil
> 
> I got the impression from somewhere on the web that cross-thread signaling is safer in Python \
> if you use pyqtSlot decorator, may that's a couple years ago so maybe I'm remembering wrong. \
> The real reason is probably that the docs on Riverbank say "Connecting a signal to a \
> decorated Python method also has the advantage of reducing the amount of memory used and is \
> slightly faster.".  
> Can you provide some details about when using pyqtSlot is really beneficial?

Sometimes it is necessary because something else communicates via the meta-object (eg. \
JavaScript).

> Are you implying that I should be able to remove all uses of pyqtSlot (as decorator or, like \
> I showed in example above, as wrapper) from our code and the code should run identically, \
> except for extra memory and slower speed (likely not noticeably slower because we don't have \
> a thread that emits huge numbers of signals)?

The way you are using it means it is being ignored - you are already using the extra memnory \
and getting the slower speed. (Assuming you haven't found the slot in the meta-object.)

Phil
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