Thanks. Will adapt for pyqt.

Thanks. It's very helpful to me.

Really good example! Thanks for sharing!

thanks a lot you saved my day

Wow! Thnx buddy!

Good example, thanks. However how to make it look like in Qt designer with same root decoration (triangle) in the left? Or replace root button with a line for example like this:

+ ------- Category 1 -------------
widgets
widgets
+ ------- Category 2 -------------
widgets
widgets

etc. thanks!

Created sample widget and plugin for Qt Designer, put it on GitHub if somebody else need this and want to improve: https://github.com/akontsevich/WidgetBox. It is ready for using however some points good to have improved:

• Style category button (or panel) closer to Qt Creator (Designer) look or like to LibreOffice Writer Properties Tool Box on the right side

• Improve pages behaviour in Qt Designer similar to QToolBox: now Designer does not change currentPageIndex PROPERTY and focus on page or category click for some reason

• Improve pages geometry resizing to content and their layout on design time and on run-time: QTreeWidget automatically increases itemWidget size height (in runtime, not design time - it remains terrible there) if contents is bigger than widget (page) height, however if size (sizeHint) is bigger - it does not decrease size to necessary minimum.

Hope for community help on these improvements.

This is jut a test on page

That's awesome ! It helps me a lot. Thanks.

Thanks for the great concept! I have reimplemented it for PyQt5:

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

class SectionExpandButton(QPushButton):
    """a QPushbutton that can expand or collapse its section
    """
    def __init__(self, item, text = "", parent = None):
        super().__init__(text, parent)
        self.section = item
        self.clicked.connect(self.on_clicked)
        
    def on_clicked(self):
        """toggle expand/collapse of section by clicking
        """
        if self.section.isExpanded():
            self.section.setExpanded(False)
        else:
            self.section.setExpanded(True)
            

class CollapsibleDialog(QDialog):
    """a dialog to which collapsible sections can be added;
    reimplement define_sections() to define sections and
        add them as (title, widget) tuples to self.sections
    """
    def __init__(self):
        super().__init__()
        self.tree = QTreeWidget()
        self.tree.setHeaderHidden(True)
        layout = QVBoxLayout()
        layout.addWidget(self.tree)
        self.setLayout(layout)
        self.tree.setIndentation(0)
        
        self.sections = []
        self.define_sections()
        self.add_sections()

    def add_sections(self):
        """adds a collapsible sections for every 
        (title, widget) tuple in self.sections
        """
        for (title, widget) in self.sections:
            button1 = self.add_button(title)
            section1 = self.add_widget(button1, widget)
            button1.addChild(section1)

    def define_sections(self):
        """reimplement this to define all your sections
        and add them as (title, widget) tuples to self.sections
        """
        widget = QFrame(self.tree)
        layout = QHBoxLayout(widget)
        layout.addWidget(QLabel("Bla"))
        layout.addWidget(QLabel("Blubb"))
        title = "Section 1"
        self.sections.append((title, widget))

    def add_button(self, title):
        """creates a QTreeWidgetItem containing a button 
        to expand or collapse its section
        """
        item = QTreeWidgetItem()
        self.tree.addTopLevelItem(item)
        self.tree.setItemWidget(item, 0, SectionExpandButton(item, text = title))
        return item

    def add_widget(self, button, widget):
        """creates a QWidgetItem containing the widget,
        as child of the button-QWidgetItem
        """
        section = QTreeWidgetItem(button)
        section.setDisabled(True)
        self.tree.setItemWidget(section, 0, widget)
        return section
        

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

Great post. I am going through some of these issues as well..

Oh, that messed up the indentation. Sorry. I have put the code on StackOverflow to copy and use:
https://stackoverflow.com/a/49941230/1413513