Singleton progress bar

main.py

"""
This is a demo of updating progress using a singleton class. This allow each class to 
report its own progress without changing the argument list so that all functions recieve
a progrees object.
"""
from threading import Thread
import time
import sys
from PyQt5 import QtCore, QtWidgets


class Singleton(type(QtCore.QObject), type):
    """Metaclass used to create a PyQt singleton"""
    def __init__(cls, name, bases, cls_dict):
        super().__init__(name, bases, cls_dict)
        cls._instance = None

    def __call__(cls, *args, **kwargs):
        if cls._instance is None:
            cls._instance = super().__call__(*args, **kwargs)
        return cls._instance


class ProgressReport(QtCore.QObject, metaclass=Singleton):
    """Create singleton class to update progress bar"""
    progress_updated = QtCore.pyqtSignal(int)

    def __init__(self):
        super().__init__()
        self.percentage = 0
    
    def updateProgress(self, progress):
        self.percentage += progress
        self.progress_updated.emit(self.percentage)

def another_function():
    report = ProgressReport()
    report.percentage = 0 # will do better than this
    for _ in range(100):
        time.sleep(0.1)
        report.updateProgress(1)


def first_function():
    report = ProgressReport()
    report.percentage = 0 # will do better than this
    for _ in range(100):
        time.sleep(0.1)
        report.updateProgress(1)


class Window(QtWidgets.QWidget):
    def __init__(self):
        super().__init__()
        self.title =  'Simple Example'
        self.resize(250, 100)

        layout = QtWidgets.QVBoxLayout()
        self.setLayout(layout)
        button1 = QtWidgets.QPushButton('First')
        button1.clicked.connect(lambda: self.buttonClicked(1))
        layout.addWidget(button1)

        button2 = QtWidgets.QPushButton('Second')
        button2.clicked.connect(lambda: self.buttonClicked(2))
        layout.addWidget(button2)

        report = ProgressReport()
        self.dialog = QtWidgets.QProgressDialog('Progress', 'Cancel', 0, 100, self)
        self.dialog.cancel()
        report.progress_updated.connect(self.dialog.setValue)
    
    def buttonClicked(self, index):
        task = first_function if index==1 else another_function
        thread = Thread(target=task)
        thread.start()
        self.dialog.show()


if __name__ == '__main__':
    app = QtWidgets.QApplication([])
    window = Window()
    window.show()
    sys.exit(app.exec())