Krdytkyu

I just began learning how to use signals and slots in PyQt5, and so I made a cute (pun intended) little program to display just one button. When the button is pressed a thread is spawned which will count from 0 to 99 and display the current count onto the button. However, when the button is counting, the program will not allow the user to spawn another thread.

I am about to actually use my knowledge for a much heavier task, and I wanted to know if there was an easier way to do what I did. Or, perhaps my way is not very efficient? Thanks in advance!

import threading

import sys

import time



from PyQt5.QtWidgets import *

from PyQt5.QtCore import *





class Application(QMainWindow):

    counter = pyqtSignal(str)

    counting = False



    def __init__(self):

        super(Application, self).__init__()



        self.button = QPushButton()

        self.button.setText('99')

        self.button.clicked.connect(self.startCounting)

        self.counter.connect(self.button.setText)



        self.layout = QVBoxLayout()

        self.layout.addWidget(self.button)

        self.frame = QFrame()

        self.frame.setLayout(self.layout)

        self.setCentralWidget(self.frame)



    def startCounting(self):

        if not self.counting:

            self.counting = True

            thread = threading.Thread(target=self.something)

            thread.start()



    def something(self):

        for x in range(100):

            self.counter.emit(str(x))

            time.sleep(.01)

        self.counting = False







if __name__ == '__main__':

    app = QApplication(sys.argv)

    window = Application()

    window.show()

    sys.exit(app.exec_())

Looks good to me!

super minor nits:

        thread = threading.Thread(target=self.something)

        thread.start()

only uses the thread variable once, so you might as well do:

        threading.Thread(target=self.something).start()

Also, the only thing you use from threading is Thread so you might as well change your import to:

from threading import Thread

and then it can be just:

Thread(target=self.something).start()

...but again, these are super minor things! It looks good to me; I may have to look at pyQT again :)

since you already used signals/slots mechanism in your program you can easily replace python thread mechanism with QThread() and make it use separate Counter() object to divide program into separate logical blocks:

# Similar to threading.thread(target=self.counter.start)

self.counterThread = QThread()

self.counter = Counter()

self.counter.moveToThread(self.counterThread)

self.counterThread.started.connect(self.counter.start)

Where the Counter() class (often named as Worker() class) is:

class Counter(QObject):

    '''

    Class intended to be used in a separate thread to generate numbers and send

    them to another thread.

    '''



    newValue = pyqtSignal(str)

    stopped = pyqtSignal()



    def __init__(self):

        QObject.__init__(self)



    def start(self):

        '''

        Count from 0 to 99 and emit each value to the GUI thread to display.

        '''



        for x in range(100):

            self.newValue.emit(str(x))

            time.sleep(.01)

        self.stopped.emit()

By using this approach you can even modify Counter() object to receive some data from the GUI on-the-fly and react accordingly.

Another minor thing is that "from package import *" was used. Usually it is considered a bad practice since you import all the contents of the package. In this case all QtCore and QtWidgets modules were imported which is ~2/3 of the PyQt5 package itself I believe))) It is more verbose but much better to use:

from PyQt5.QtWidgets import QMainWindow, QPushButton, QVBoxLayout, QFrame, QApplication

from PyQt5.QtCore import pyqtSignal, QObject, QThread

or:

from PyQt5 import QtWidgets, QtCore

...

self.button = QtWidgets.QPushButton()

That way you and other code readers always know which object belongs to which package as well.

Here is the complete code rewritten according to those notes:

'''

https://codereview.stackexchange.com/questions/138992/simple-pyqt5-counting-gui

'''



import sys

import time



from PyQt5.QtWidgets import QMainWindow, QPushButton, QVBoxLayout, QFrame, QApplication

from PyQt5.QtCore import pyqtSignal, QObject, QThread



class Counter(QObject):

    '''

    Class intended to be used in a separate thread to generate numbers and send

    them to another thread.

    '''



    newValue = pyqtSignal(str)

    stopped = pyqtSignal()



    def __init__(self):

        QObject.__init__(self)



    def start(self):

        '''

        Count from 0 to 99 and emit each value to the GUI thread to display.

        '''



        for x in range(100):

            self.newValue.emit(str(x))

            time.sleep(.01)

        self.stopped.emit()





class Application(QMainWindow):

    def __init__(self):

        QMainWindow.__init__(self)



        # Configuring widgets        

        self.button = QPushButton()

        self.button.setText('99')

        self.layout = QVBoxLayout()

        self.layout.addWidget(self.button)

        self.frame = QFrame()

        self.frame.setLayout(self.layout)

        self.setCentralWidget(self.frame)



        # Configuring separate thread

        self.counterThread = QThread()

        self.counter = Counter()

        self.counter.moveToThread(self.counterThread)



        # Connecting signals

        self.button.clicked.connect(self.startCounting)

        self.counter.newValue.connect(self.button.setText)

        self.counter.stopped.connect(self.counterThread.quit)

        self.counterThread.started.connect(self.counter.start)





    def startCounting(self):

        '''

        Start counting if no other counting is done.

        '''



        if not self.counterThread.isRunning():

            self.counterThread.start()





if __name__ == '__main__':

    app = QApplication(sys.argv)

    window = Application()

    window.show()

    sys.exit(app.exec_())

Keep up the good work and best wishes.