[PySide] What if a slot is not decorated with @Slot()?

Zhao Lee redstone-cold at 163.com
Sat Nov 19 03:47:38 CET 2022

Thanks Chris!
The question originated from the issue :
In my project, self.sender() in the downloadFinished slot sometimes returns None instead of QNetworkReply, if comment the @Slot() ahead it seems to always return QNetworkReply - works well. The same issue also happened to the slot connected to the finished signal of QProcess. But the issue didn't happen for the PyQt5 version in my project. I reduced my senario to the following lite demo, but haven't seen the issue happened again, very strange !
Test environment : Python 3.9.13 on win11 64bit, latest PySide6.
from PySide6.QtCore import*
from PySide6.QtCore import Slot
from PySide6.QtCore import Signal
from PySide6.QtGui import*
from PySide6.QtWidgets import*
from PySide6.QtNetwork import*

import sys


    def__init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.manager =QNetworkAccessManager(self)



        url ='https://download-cdn.jetbrains.com/python/pycharm-professional-2022.2.3.exe'
        request =QNetworkRequest(QUrl(url))
        reply =self.manager.get(request)
        self.reply2DownloadFileTuple[reply] =None

        reply.downloadProgress.connect(self.downloadProgress)#, Qt.QueuedConnection
    defdownloadProgress(self, bytesReceived, bytesTotal):
        reply =self.sender()

        reply =self.sender()

        ifnotisinstance(reply, QNetworkReply):
            print('not QNetworkReply')

        # er = reply.error()
        # if er == QNetworkReply.NetworkError.NoError:

        #     bytes_string = reply.readAll()
        #     print(str(bytes_string, 'utf-8'))

        # else:
        #     print("Error occured: ", er)
        #     print(reply.errorString())

        # QCoreApplication.quit()


    win =Example()

if __name__ =='__main__':
At 2022-11-18 19:02:29, "Christian Tismer-Sperling" <tismer at stackless.com> wrote:
>Hi Zhao,
>there is a configuration problem between Qt and PySide signals and
>slots. The Qt signals and slots are assigned once at compile time.
>On PySide, initialization is different since some things happen
>earlier or later. There *can* be situations constructed which go wrong,
>although doing that is difficult. You will not want to run into these
>problems by accident.
>Please believe me as one of the implementers:
>There is only one safe way to create reliable signals and slots.
>Use the decorator!
>Cheers - Chris
>On 16.11.22 15:18, Zhao Lee wrote:
>> I initially expect that the aim of the decorator @Slot() is to make 
>> things easier like this
>> https://uwsgi-docs.readthedocs.io/en/latest/PythonDecorators.html#notes 
>> <https://uwsgi-docs.readthedocs.io/en/latest/PythonDecorators.html#notes>
>> and without the decorator , you'd expect write a little more code like
>> https://uwsgi-docs.readthedocs.io/en/latest/Signals.html?#timers 
>> <https://uwsgi-docs.readthedocs.io/en/latest/Signals.html?#timers>
>> But decorators in PySide become a little different. I know the decorator 
>> can make the signal and slot connection a bit easier in PyQt in this way
>> */    @Slot(QModelIndex)/*
>> */    def on_downloadedView_doubleClicked(self, index) :/*
>> */           pass/*
>> But I still doubt the necessity of the decorator here if we write the 
>> slot method name in this way. I wonder if it is possible to simplify the 
>> mechanism in PySide like that in the above example of uwsgi without 
>> requiring it is mandatory(In fact as I posted in last email, it seems 
>> still ok without the decorator, although the doc states it is mandatory 
>> to exist).
>Christian Tismer-Sperling    :^)   tismer at stackless.com
>Software Consulting          :     http://www.stackless.com/
>Strandstraße 37              :     https://github.com/PySide
>24217 Schönberg              :     GPG key -> 0xFB7BEE0E
>phone +49 173 24 18 776  fax +49 (30) 700143-0023
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