[FIXED] How do I programmatically change the parent of a layout

Issue

I want to be able to move a layout to another layout based on a user input. I have the following code which does not appear to work for me. If I switch lines 31 and 34 so that they operate on the widget rather than the layout then I get the expected behaviour but I am hoping to operate on all widgets within a layout by just moving the layout.

import sys

from PyQt5.QtWidgets import QPushButton, QWidget, QHBoxLayout, QLabel, QApplication, QVBoxLayout


class b(QWidget):
    def __init__(self, name):
        super(b, self).__init__()
        self.layout = QVBoxLayout(self)
        lbl_1 = QLabel(name)
        self.layout.addWidget(lbl_1)

class a(QWidget):
    def __init__(self):
        super(a, self).__init__()
        self.layout = QHBoxLayout(self)
        self.widget_1 = b('widget 1')
        self.widget_2 = b('widget 2')
        self.layout.addWidget(self.widget_1)
        self.layout.addWidget(self.widget_2)

        self.button_layout = QHBoxLayout()
        self.move_layout = QPushButton('Move to other layout')
        self.move_layout.clicked.connect(lambda: self.move_button())
        self.button_layout.addWidget(self.move_layout)
        self.widget = 'widget_2'
        self.widget_2.layout.addLayout(self.button_layout)

    def move_button(self):
        if self.widget == 'widget_2':
            self.widget_1.layout.addLayout(self.button_layout)
            self.widget = 'widget_1'
        else:
            self.widget_2.layout.addLayout(self.button_layout)
            self.widget = 'widget_2'
        print('moved widget to {}'.format(self.widget))

if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = a()
    window.show()
    sys.exit(app.exec_())

Edit: to clarify, In the example above, the layout I want to move (self.button_layout) is a child layout of self.widget_2.layout. When I click the pushbutton, I want the self.button_layout to be set as a child layout of self.widget_1.layout. Essentially it will do what the code below does but using addLayout instead of addWidget.

import sys

from PyQt5.QtWidgets import QPushButton, QWidget, QHBoxLayout, QLabel, QApplication, QVBoxLayout


class b(QWidget):
    def __init__(self, name):
        super(b, self).__init__()
        self.layout = QVBoxLayout(self)
        lbl_1 = QLabel(name)
        self.layout.addWidget(lbl_1)

class a(QWidget):
    def __init__(self):
        super(a, self).__init__()
        self.layout = QHBoxLayout(self)
        self.widget_1 = b('widget 1')
        self.widget_2 = b('widget 2')
        self.layout.addWidget(self.widget_1)
        self.layout.addWidget(self.widget_2)

        self.button_layout = QHBoxLayout()
        self.move_layout = QPushButton('Move to other layout')
        self.move_layout.clicked.connect(lambda: self.move_button())
        self.button_layout.addWidget(self.move_layout)
        self.widget = 'widget_2'
        self.widget_2.layout.addLayout(self.button_layout)

    def move_button(self):
        if self.widget == 'widget_2':
            self.widget_1.layout.addWidget(self.move_layout)
            self.widget = 'widget_1'
        else:
            self.widget_2.layout.addWidget(self.move_layout)
            self.widget = 'widget_2'
        print('moved widget to {}'.format(self.widget))

if __name__ == '__main__':
    app = QApplication(sys.argv)
    window = a()
    window.show()
    sys.exit(app.exec_())

Solution

The problem is that if a layout has a parent then it cannot be changed as the error message indicates:

QLayout::addChildLayout: layout "" already has a parent

One possible solution is to remove the parent:

def move_button(self):
    self.button_layout.setParent(None)
    if self.widget == "widget_2":
        self.widget_1.layout.addLayout(self.button_layout)
        self.widget = "widget_1"
    else:
        self.widget_2.layout.addLayout(self.button_layout)
        self.widget = "widget_2"
    print("moved widget to {}".format(self.widget))

Another alternative is to place the layout in a QWidget that is the container and that place it in the required layout:

class a(QWidget):
    def __init__(self):
        super(a, self).__init__()
        layout = QHBoxLayout(self)
        self.widget_1 = b("widget 1")
        self.widget_2 = b("widget 2")
        layout.addWidget(self.widget_1)
        layout.addWidget(self.widget_2)

        self.container = QWidget()
        container_layout = QHBoxLayout(self.container)
        button = QPushButton("Move to other layout")
        button.clicked.connect(self.move_button)
        container_layout.addWidget(button)

        self.widget = "widget_1"
        self.move_button()

    def move_button(self):
        if self.widget == "widget_2":
            self.widget_1.layout.addWidget(self.container)
            self.widget = "widget_1"
        else:
            self.widget_2.layout.addWidget(self.container)
            self.widget = "widget_2"
        print("moved widget to {}".format(self.widget))

Answered By - eyllanesc