Why those widgets with layouts don't work

Question

This is a schema for what I want:

This is what I try to do. Black line its Window. I want to have a QWidget (red line) that will hold a vertical list of QWidgets. I don't know where I'm making mistake. Does it work differently then what I think?

Here's code:

from PyQt5.QtWidgets import *

class MainWindow(QWidget):
    def __init__(self):
        super().__init__()


        mainLay = QVBoxLayout()
        self.setLayout(mainLay)

        # QWidget
        listW = QWidget()
        listW.setStyleSheet('background: lightgreen')
        mainLay.addWidget(listW)
        listLay = QHBoxLayout()
        mainLay.addLayout(listLay)

        row1 = QLabel("1")
        row1.setStyleSheet('background: green')
        listLay.addWidget(row1)

        row2 = QLabel("2")
        row2.setStyleSheet('background: red')
        listLay.addWidget(row2)

        self.resize(400, 300)


if __name__ == "__main__":

    import sys
    app = QApplication(sys.argv)
    window = MainWindow()
    window.show()
    sys.exit(app.exec_())

Here's how it looks like:

Answer 1

You are creating a QHBoxLayout ("H" for horizontal) and adding 2 widgets, and that layout you are placing in the QVBoxLayout ("V" for vertical).

You only need a QVBoxLayout and there place all the widgets:

class MainWindow(QWidget):
    def __init__(self):
        super().__init__()

        listW = QWidget()
        listW.setStyleSheet("background: lightgreen")

        row1 = QLabel("1")
        row1.setStyleSheet("background: green")

        row2 = QLabel("2")
        row2.setStyleSheet("background: red")

        mainLay = QVBoxLayout(self)
        mainLay.addWidget(listW)
        mainLay.addWidget(row1)
        mainLay.addWidget(row2)

        self.resize(400, 300)

If you want to have a container QWidget then add it through another layout:

class MainWindow(QWidget):
    def __init__(self):
        super().__init__()

        container = QWidget(styleSheet="background: salmon")

        row1 = QLabel("1", styleSheet="background: lightgreen")
        row2 = QLabel("2", styleSheet="background: green")
        row3 = QLabel("3", styleSheet="background: red")

        container_layout = QVBoxLayout(self)
        container_layout.addWidget(container)

        mainLay = QVBoxLayout(container)
        mainLay.addWidget(row1)
        mainLay.addWidget(row2)
        mainLay.addWidget(row3)

        self.resize(400, 300)