Converting c++ class to python class

[Panoss]

I 'm trying to convert a c++ class to python class.

My class 's c++ code (in epnccombomodel.cpp file):

#include "epnccombomodel.h"
 
EPNCComboModel::EPNCComboModel(QObject *parent) : QAbstractProxyModel(parent)
{
}

My class 's python code (in epnccombo.py file):

from PyQt4.QtCore import QObject
from PyQt4.QtGui import QAbstractProxyModel
 
 
class EPNCComboModel(QObject) :
    def __init__(self, parent):
        QAbstractProxyModel(EPNCComboModel, self).__init__(parent)

But I get an error (TypeError: init() missing 1 required positional argument: 'parent') on initialization.
I initialize it this way: EPNCproxyModel = EPNCComboModel()

First of all, this line: EPNCComboModel::EPNCComboModel(QObject *parent) : QAbstractProxyModel(parent)
What exactly is it saying?
"Create a Class deriving from QObject"? (child of QObject)
And variable 'parent' equals to this QObject?

[SGaist]

Hi,

Do you mean you just want to translate or do you want to create a wrapper on top of your C++ code ?

[jsulm]

@Panoss said in Converting c++ class to python class:

def init(self, parent)

Your constructor requires a non optional parameter, so you have to give one:

EPNCproxyModel = EPNCComboModel(some_parent_object)

Parent can be nullptr in C++ if you do not want to have a parent by default (but you can still provide one if needed):

EPNCComboModel(QObject *parent=nullptr)

In this case you can omit parent.
In Python:

def __init__(self, parent=None):

Read this about child/parent: http://doc.qt.io/qt-5.9/objecttrees.html

[Panoss]

@SGaist said in Converting c++ class to python class:

Hi,

Do you mean you just want to translate or do you want to create a wrapper on top of your C++ code ?

Not a wrapper of C++.
I want to create a python class that will behave excactly like my C++ function.
So I thought the best way would be to 'translate' C++ to Python.

Up to here, I think we are ok:

class EPNCComboModel(QObject):
    def __init__(self, parent=None):

But QAbstractProxyModel has to 'get into the game' somehow.

[SGaist]

No you're not. Why doesn't EPNCComboMode inherit QAbstractProxyModel ?

[Panoss]

This is what I finally did, I made my class inherit QAbstractProxyModel.

Now, another part of the class' code.
How do I 'translate' this:

QModelIndex EPNCComboModel::mapFromSource(const QModelIndex & sourceIndex) const

to python?

The hard part for me is this: QModelIndex & sourceIndex
Maybe in python becomes??:

sourceIndex

[SGaist]

It's then just

mapped = model.mapFromSource(sourceIndex)

[edit: Fixed variable name SGaist]

[Panoss]

Hi SGaist.
what is map.p?

I think the correct code is:

def mapToSource(self, proxyIndex):

It seems to work. ('self' is like 'this' in C++. It's used (in a class' function) in order to refer to the class)

[SGaist]

That was a typo.

Indeed the python function signature is def mapToSource(self, proxyIndex):.

[Panoss]

How about this?
This is from optiongroup.h file:

class OptionGroup : public QWidget
{
Q_OBJECT
Q_PROPERTY(int currentSelection READ currentSelection WRITE setCurrentSelection USER true)

This is from optiongroup.cpp file:

OptionGroup::OptionGroup(QWidget *parent) :QWidget(parent), currentSelection_(-1)
{
}

How can I convert it to python?

[Panoss]

How does this look? Am I on the right way?

class OptionGroup(QtGui.QWidget) :
    def __init__(self, parent):
        super(OptionGroup, self).__init__(parent)
        self.currentSelection_ = -1
        self.currentSelection = pyqtProperty(int, self.getCurrentSelection, self.setCurrentSelection)

So this:

Q_PROPERTY(int currentSelection READ currentSelection WRITE setCurrentSelection USER true)

equals to this?

self.currentSelection = pyqtProperty(int, self.getCurrentSelection, self.setCurrentSelection)

[SGaist]

You have an example in the PyQt5 documentation.

[Panoss]

The instances of this class are mapped to a QWidgetDataMapper.
The problem is that it seems that they don't 'bind' to the QWidgetDataMapper.

In the C++ class, I think, that this job does this line:

OptionGroup::OptionGroup(QWidget *parent) :QWidget(parent), currentSelection_(-1)

I think it means: 'set property for mapping the property named "currentSelection_" '.

So I think (again :) ) that my problem is that I can't do the same in Python.

[SGaist]

You have to mark the property as USER like explained in the QDataWidgetMapper documentation.

[Panoss]

I changed this line from:

currentSelection = pyqtProperty(int, currentSelection, setCurrentSelection)

...to:

currentSelection = pyqtProperty(int, currentSelection, setCurrentSelection, user = True)

and it works! I can't believe I was struggling for so many days for 2 f***ng words!

SGaist you can't imagine how much you helped me. THANK YOU!