QWidget::setLayout: Attempting to set QLayout "" on Window "", which already has a layout

by Martin Fitzpatrick Last updated FAQ
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I am a Beginner. I do not understand this error message. Who can explain it to me. :-)

Attempting to set QLayout "" on Window "", which already has a layout

python 
from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import (
    QApplication, QWidget, QMainWindow,
    QVBoxLayout, QHBoxLayout, QFormLayout, QGridLayout, QStackedLayout,
    QPushButton, QComboBox, QLineEdit, QCheckBox, QRadioButton,
)
class Window(QWidget):
    def __init__(self):
        super().__init__()

        layVer = QVBoxLayout()
        self.comBox = QComboBox()
        self.comBox.addItems(["One", "Two", "Three"])
        self.comBox.activated.connect(lambda x: self.onComBox(x))
        layVer.addWidget(self.comBox)
        self.setLayout(layVer)

        layHor = QHBoxLayout()
        self.cheBox1 = QCheckBox("A")
        layHor.addWidget(self.cheBox1)
        self.setLayout(layHor)

        layVer.addLayout(layHor)

    def onCheBox(self, s):
        print(s)

    def onComBox(self, s):
        print(s, self.comBox.currentText())

if __name__ == "__main__":
    app = QApplication([])
    win = Window()
    win.show()
    app.exec_()

PedanticHacker

Firstly, delete the line self.setLayout(layVer)

then fix

python 
self.setLayout(layHor)

layVer.addLayout(layHor)

to be

python 
layVer.addLayout(layHor)

self.setLayout(layVer)

Martin Fitzpatrick

This error occurs because you're trying to set a layout on a QMainWindow. The QMainWindow is a special widget which has a built-in layout, to handle things link menus, toolbars and dock widgets.

For windows based on QMainWindow you can only set a central widget -- that is, the widget that appears in the center of the window. But if you remember from the PyQt5 layouts tutorial you can set a layout on an empty QWidget and add anything you want to it that way.

So the trick is: for controlling the layout of a mainwindow we first create a QWidget to act as a "container", use that widget as our central widget and apply the layout to it to add other widgets.

_Ali Sanawi Garrousi__

Merci now it works!

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For a complete guide to building GUI applications with Python, see our PyQt6 tutorial. Using another library? We also have a PyQt5 tutorial, PySide6 tutorial and PySide2 tutorial.

Martin Fitzpatrick

QWidget::setLayout: Attempting to set QLayout "" on Window "", which already has a layout was written by Martin Fitzpatrick .

Martin Fitzpatrick has been developing Python/Qt apps for 8 years. Building desktop applications to make data-analysis tools more user-friendly, Python was the obvious choice. Starting with Tk, later moving to wxWidgets and finally adopting PyQt. Martin founded PythonGUIs to provide easy to follow GUI programming tutorials to the Python community. He has written a number of popular https://www.martinfitzpatrick.com/browse/books/ on the subject.

QWidget::setLayout: Attempting to set QLayout "" on Window "", which already has a layout was published in faq on (updated ) . Feedback & Corrections can be submitted here.