Collapsible widget using PyQt5.

collapsible_widget.py

import sys
from PyQt5.QtWidgets import QFrame, QWidget, QHBoxLayout, QVBoxLayout, QLabel, QPushButton, QApplication, QMainWindow
from PyQt5.QtCore import Qt
from PyQt5.QtGui import QIcon
import collapsible_widget_resources

VERTICAL_ARROW_PATH = ":/vertical_arrow_collapsible.png"
HORIZONTAL_ARROW_PATH = ":/horizontal_arrow_collapsible.png"


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

        self.setStyleSheet("background-color: #dcdee0;")
        self.setCentralWidget(MainWidget())

        self.show()


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

        self.setLayout(QVBoxLayout())
        self.layout().setSpacing(0)
        # The below line will make that when you collapse a widget
        # and uncollapse it kept it's position (at the top).
        self.layout().setAlignment(Qt.AlignTop)
       
        collapsible_widget2 = CollapsibleWidget(title="Nested collapsible widget")
        collapsible_widget2.addWidget(QPushButton('c'))
        collapsible_widget2.addWidget(QPushButton('d'))
        collapsible_widget2.addWidget(QPushButton('e'))

        collapsible_widget1 = CollapsibleWidget(title="Collapsible ")
        collapsible_widget1.addWidget(QPushButton('a'))
        collapsible_widget1.addWidget(QPushButton('b'))
        collapsible_widget1.addWidget(collapsible_widget2)

        self.layout().addWidget(collapsible_widget1)


class CollapsibleWidget(QWidget):
    def __init__(self, parent=None, title=None):
        super().__init__()
        
        self.is_collasped = True

        self.title_frame = self.CollapseButton(title, self.is_collasped)        
        self.title_frame.clicked.connect(self.toggle_collapsed)

        self.setLayout(QVBoxLayout())
        self.layout().addWidget(self.title_frame)
        self.layout().addWidget(self.init_content())

    def init_content(self):
        self.content = QWidget()
        self.content_layout = QVBoxLayout()

        self.content.setLayout(self.content_layout)
        self.content.setVisible(not self.is_collasped)

        return self.content

    def addWidget(self, widget):
        self.content_layout.addWidget(widget)
   
    def toggle_collapsed(self):
        self.content.setVisible(self.is_collasped)
        self.is_collasped = not self.is_collasped
        self.title_frame.update_arrow(self.is_collasped)


    class CollapseButton(QPushButton):
        def __init__(self, title="", is_collasped=True, parent=None):
            super().__init__()

            self.setText(title)
            self.update_arrow()

            self.setStyleSheet(
            """
            *{
            	padding: 3px 5px 3px 5px;
            	text-align: left;
            	border: none;
            	background-color: #dcdee0;
            }
            *:hover {
            	background-color: #c7cccf;
            }
            """
            )


        def update_arrow(self, is_collasped=True):
        	if is_collasped:
	            self.setIcon(QIcon(HORIZONTAL_ARROW_PATH))
	        elif not is_collasped:
	            self.setIcon(QIcon(VERTICAL_ARROW_PATH))


if __name__ == '__main__':
    app = QApplication(sys.argv)
    main_window = MainWindow()
    sys.exit(app.exec_())

collapsible_widget_resources.py

# -*- coding: utf-8 -*-

# Resource object code
#
# Created by: The Resource Compiler for PyQt5 (Qt v5.15.2)
#
# WARNING! All changes made in this file will be lost!

from PyQt5 import QtCore

qt_resource_data = b"\
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qt_resource_struct_v2 = b"\
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qt_version = [int(v) for v in QtCore.qVersion().split('.')]
if qt_version < [5, 8, 0]:
    rcc_version = 1
    qt_resource_struct = qt_resource_struct_v1
else:
    rcc_version = 2
    qt_resource_struct = qt_resource_struct_v2

def qInitResources():
    QtCore.qRegisterResourceData(rcc_version, qt_resource_struct, qt_resource_name, qt_resource_data)

def qCleanupResources():
    QtCore.qUnregisterResourceData(rcc_version, qt_resource_struct, qt_resource_name, qt_resource_data)

qInitResources()

Remember to download both files collapsible_widget.py and collapsible_widget_resources.py.