[PyQt] pyqtSlot

oliver oliver.schoenborn at gmail.com
Thu Aug 25 17:01:46 BST 2016

To be clear, our app has a backend Qt thread.

Open Source contributions: PyPubSub <http://pubsub.sf.net/>, nose2pytest
<https://github.com/schollii/nose2pytest>, Lua-iCxx
<http://lua-icxx.sf.net/>, iof <http://iof.sf.net/>
StackOverflow <http://stackoverflow.com/users/869951/schollii> contributions

On Thu, Aug 25, 2016 at 12:00 PM, oliver <oliver.schoenborn at gmail.com>

> On Thu, Aug 25, 2016 at 11:25 AM, Phil Thompson <
> phil at riverbankcomputing.com> wrote:
>> On 25 Aug 2016, at 2:24 pm, oliver <oliver.schoenborn at gmail.com> wrote:
>> >
>> >
>> >
>> > On Thu, Aug 25, 2016 at 8:40 AM, Phil Thompson <
>> phil at 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? 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)?
> Oliver
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