Qt for Python UsingQtProperties

PySide2 provides a Property function which allows for declaring properties that simultaneously behave both as Qt and Python properties, and have their setters and getters defined as Python functions.

A short example illustrating defining and accessing a Qt property from Python is given below:

from PySide2.QtCore import QObject, Property                                                        
                                                                                                    
class MyObject(QObject):                                                                            
    def __init__(self,startval=42):                                                                 
        QObject.__init__(self)                                                                      
        self.ppval = startval                                                                       
                                                                                                    
    def readPP(self):                                                                                   
        return self.ppval                                                                               
                                                                                                    
    def setPP(self,val):                                                                                
        self.ppval = val                                                                                
                                                                                                    
    pp = Property(int, readPP, setPP)     
                                                              
obj = MyObject()                                                                                    
obj.pp = 47                                                                                         
print(obj.pp)

Properties in QML expressions

If you are using properties of your objects in QML expressions, QML requires the property to be NOTIFYable or constant. If the value of the property changes over time, you should apply NOTIFYable using a simple signal:

from PySide2.QtCore import QObject, Signal, Property

class Person(QObject):
    def __init__(self, name):
        QObject.__init__(self)
        self._person_name = name

    def _name(self):
        return self._person_name

    @Signal
    def name_changed(self):
        pass

    name = Property(str, _name, notify=name_changed)

You can use constant if your value is immutable. Use it as follows:

from PySide2.QtCore import QObject, Signal, Property

class Person(QObject):
    def __init__(self, name):
        QObject.__init__(self)
        self._person_name = name

    def _name(self):
        return self._person_name

    name = Property(str, _name, constant=True)