Python Widget with SizePolicy

Why the sizePolicy doesn't affect on widgets that aren't in layout?

here is an example:

from PyQt5 import QtWidgets

app = QtWidgets.QApplication([])
window = QtWidgets.QWidget()
window.setGeometry(50, 50, 500, 300)

test_widget = QtWidgets.QWidget(window)
test_widget.setMinimumSize(100, 100)
test_widget.setStyleSheet("background-color:red")
size_policy = QtWidgets.QSizePolicy(QtWidgets.QSizePolicy.Minimum, QtWidgets.QSizePolicy.Minimum)
test_widget.setSizePolicy(size_policy)


window.show()
app.exec()

But that doesn't work, if you changed the main window size the red box still has the same size.

So how can I make that red box resizeable when the parent (main window) is changing.

NOTE: I don't want to use Layouts for some reason.

Solution

I'm not sure I completely understand your GUI design but you should note that a single cell (as defined by a row/column pair) in a QGridLayout can be occupied by more than a single widget. A (very) simple example demonstrates this...

#!/usr/local/bin/python3
import os
import sys

from PySide2.QtWidgets import QApplication, QGridLayout, QLabel, QPushButton, QWidget
from PySide2.QtCore import Qt

class widget(QWidget):
    def __init__ (self, parent = None):
        super(widget, self).__init__(parent)
        gl = QGridLayout(self)
        pb = QPushButton("Show/Hide Menu")
        self.menu = QLabel("Menu goes here...")
        self.menu.setAlignment(Qt.AlignCenter)
        self.menu.setStyleSheet("background-color: #40800000;")
        canvas = QLabel("Canvas")
        canvas.setAlignment(Qt.AlignCenter)
        canvas.setStyleSheet("background-color: #40000080;")
        gl.addWidget(pb, 0, 0)
        gl.addWidget(canvas, 0, 0, 2, 2)
        pb.raise_()
        pb.clicked.connect(self.toggle_menu)
        gl.addWidget(self.menu, 1, 0)
        self.menu.hide()
    def toggle_menu (self, checked):
        self.menu.setVisible(not self.menu.isVisible())

if __name__ == '__main__':
    app = QApplication([])
    w = widget()
    w.show()
    app.exec_()

[I've used PySide2 as I don't have PyQt5 installed.]

So if I have understood correctly then I don't see why you can't make use of a QGridLayout. Could save you a lot of work.