[PyQt] QWidget call other __init__ methods, but why?

[Barry Scott]

> On 28 Jun 2016, at 17:01, Phil Thompson <phil at riverbankcomputing.com> wrote:
> 
> On 28 Jun 2016, at 4:52 pm, Barry Scott <barry at barrys-emacs.org> wrote:
>> 
>> Here we have a class that I use in my app. I just fixed a bug
>> where wbTrackedModeless.__init__ was called twice as proved
>> by using traceback.print_stack().
>> 
>> class WbTrackedModelessQWidget(QtWidgets.QWidget, WbTrackedModeless):
>>   def __init__( self ):
>>       QtWidgets.QWidget.__init__( self, None ) # line 50
>>   def closeEvent( self, event ):
>>       WbTrackedModeless.closeEvent( self, event )
>> 
>>       super().closeEvent( event )
>> 
>> From the definition it looks like wbTrackedModeless.__init__ is 
>> not called.
>> 
>> However here is the stack:
>> 
>> File "wb_scm_main.py", line 21, in <module>
>>   sys.exit( wb_main.main( wb_scm_app.WbScmApp, sys.argv ) )
>> File "/Users/barry/wc/git/scm-workbench/Source/Common/wb_main.py", line 52, in main
>>   rc = app.exec_()
>> File "/Users/barry/wc/git/scm-workbench/Source/Git/wb_git_ui_actions.py", line 172, in treeTableActionGitLogHistory
>>   self.main_window.callTreeOrTableFunction( self.treeActionGitLogHistory, self.tableActionGitLogHistory )
>> File "/Users/barry/wc/git/scm-workbench/Source/Scm/wb_scm_main_window.py", line 617, in callTreeOrTableFunction
>>   return fn_tree()
>> File "/Users/barry/wc/git/scm-workbench/Source/Git/wb_git_ui_actions.py", line 347, in treeActionGitLogHistory
>>   self.main_window.getQIcon( 'wb.png' ) )
>> File "/Users/barry/wc/git/scm-workbench/Source/Git/wb_git_log_history.py", line 162, in __init__
>>   super().__init__()
>> File "/Users/barry/wc/git/scm-workbench/Source/Common/wb_tracked_qwidget.py", line 50, in __init__
>>   QtWidgets.QWidget.__init__( self, None )
>> File "/Users/barry/wc/git/scm-workbench/Source/Common/wb_tracked_qwidget.py", line 29, in __init__
>>   self.__trackWidget()
>> File "/Users/barry/wc/git/scm-workbench/Source/Common/wb_tracked_qwidget.py", line 34, in __trackWidget
>>   traceback.print_stack()
>> 
>> This shows that QtWidgets.QWidget.__init__( self, None ) called WbTrackedModeless.__init__()
>> (__trackWidget is first line of __init__ at line 29).
>> 
>> I guess Phil this is a question for you.
>> 
>> Why does PyQt call __init__ if there is multiple inheritance? Is this a bug in PyQt?
> 
> See...
> 
> http://pyqt.sourceforge.net/Docs/PyQt5/multiinheritance.html

Phil,

I must be missing something important.

https://rhettinger.wordpress.com/2011/05/26/super-considered-super/ shows the base classes being called
via explicit super() calls. I cannot find a way to have super() call more then one function.

If I recreate your Person example in pure python I do not see Age.__init__ called.
It seems that you are doing something unique in PyQt to get Age called.

Here is the code I used to test the idea in Hettinger’s blog based on your example
(but avoiding the PyQy5 implementation):

class QObject(object):
    def __init__( self ):
        print( 'instance of QObject.__init__' )

class Age(object):
    def __init__( self, age=0, **kwds ):
        print( 'instance of Age.__init__' )

        self.age = age

class Person(QObject, Age):
    def __init__( self, name='', **kwds ):
        print( 'instance of Person.__init__' )
        super().__init__()

        self.name = name

x = Person( name='Barry', age=21 )
print( x.name )
print( x.age )

Output:

$ python3.5 qqq.py
instance of Person.__init__
instance of QObject.__init__
<__main__.Person object at 0x1019e6668>

Barry


> 
> Phil