如何扩展一个类实例？

Question

I have an instance..

groupCell = QtGui.QGroupBox()
print groupCell.title() #this class has a method title()

I am not able to change anything of this instance, it comes how it is...

I need to extend this instance (add some methods etc.)

class GroupBoxWithCheckbox (QtGui.QGroupBox):
    def __init__(self, basegroupbox, checkbox):
        #something like self = basegroupbox ?
        self.checkbox = checkbox
    def method(self):
        pass

and finally

groupCellWithCheckBox = GroupBoxWithCheckbox(groupCell, checkbox)
print groupCellWithCheckBox.title()

I have to get the same title as with groupCell.

Answer 1

You can define a new class extending QtGui.QGroupBox that looks like this:

class GroupBoxWithCheckbox(QtGui.QGroupBox):

    def __init__(self, checkbox):
        super(GroupBoxWithCheckbox, self).__init__()
        self.checkbox = checkbox

    def method(self):
        pass

Then you can simply make groupCell an instance of this class, and pass in a checkbox when you initialise it:

groupCell = GroupBoxWithCheckbox(checkbox)

That will have the same effect as what you are trying to do here.

---

Edit, since new information has been provided:

Since we're talking Python here, you can dynamically add things to any instance you want. It's totally possible to do this:

groupCell.checkbox = checkbox

Even if the groupCell doesn't have a checkbox property . The property will be added when you set it, as in my snippet above. You could use that to do what you want. It's kind of a weird thing to do, and I don't recommend it, but it would work. The alternative is to make a wrapper class of some sort:

class GroupBoxWithCheckbox(object):
    def __init__(self, groupbox, checkbox):
        self.groupbox = groupbox
        self.checkbox = checkbox

groupCell = GroupBoxWithCheckbox(groupCell, checkbox)

And then any time you want to access a method of the original GroupBox, you can do something like

groupCell.groupbox.title()

groupCell.groupbox will contain all of the methods that the original GroupBox did, but you'll also have access to groupCell.checkbox .

The latter solution is what I would implement if I were coding this.

Answer 2

Call base class constructor using super :

class GroupBoxWithCheckbox(QtGui.QGroupBox):
    def __init__(self, basegroupbox, checkbox):
        super(GroupBoxWithCheckbox, self).__init__()
        self.checkbox = checkbox
        self.basegroupbox = basegroupbox
    def title(self):
        return self.basegroupbox.title()