Why are my labels stacking on top of each other inside my QHBoxLayout?

Question

Simply enough, I want to add two labels inside an horizontal box layout using Python's PYQT5.

When I execute this code, the two labels appear on top of each other, even though adding them to a QHBoxLayout should position them from left to right.

How can I fix this?

• Compiler : Python 3.7.4 32 bit
• IDE : Visual Studio Code
• OS : Windows 10

my code:

import sys
from PyQt5.QtCore import Qt
from PyQt5.QtWidgets import *
from PyQt5.QtGui import *

class Interface(QMainWindow):
    def __init__(self):
        super().__init__()

        self.title = 'debug'
        self.mainLayout = QHBoxLayout()
        self.initGUI()

    def initGUI(self):
        self.setGeometry(0,0,200,200)
        self.setFixedSize(self.size())
        self.setWindowTitle(self.title)

        label1 = QLabel('test 1',self)
        label2 = QLabel('test 2',self)
        self.mainLayout.addWidget(label1)
        self.mainLayout.addWidget(label2)

        self.setLayout(self.mainLayout)
        self.show()    

    def close_application(self):
        sys.exit()

if __name__ == '__main__':
    app = QApplication([])
    window = Interface()
    sys.exit(app.exec_())

Answer 1

Explanation:

QMainWindow is a special widget that has a default layout:

that does not allow to establish another layout and clearly indicates the error message that is obtained when executing your code in the terminal/CMD:

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

So when the layout is not established, it does not handle the position of the QLabels, and you, when passing as a parent to window-self, both will be set in the window in the top-left position.

Solution:

As the docs points out, you must create a central widget that is used as a container and then set the layout:

def initGUI(self):
    self.setGeometry(0,0,200,200)
    self.setFixedSize(self.size())
    self.setWindowTitle(self.title)

    central_widget = QWidget() # <---
    self.setCentralWidget(central_widget) # <---

    label1 = QLabel('test 1')
    label2 = QLabel('test 2')
    self.mainLayout.addWidget(label1)
    self.mainLayout.addWidget(label2)

    central_widget.setLayout(self.mainLayout) # <---
    self.show()