FTP download with text label showing the current status of the download

Question

I made a GUI in which after I click "Download" button the program will download files from FTP server. When doing that I want the label to update e.g: "Connecting..." -> "Downloading..." -> "Downloaded!" I tried doing it with threading module but it seems to not work:

def updater(self):
    self.updateStatusText.setText("Status: Connecting...")

    thread = threading.Thread(target=self.download)
    thread.start()

    while thread.isAlive():
        self.updateStatusText.setText("Status: Still Downloading...")


def download(self):
    ftp = FTP('testdomain.com')
    ftp.login(user='username', passwd='password')

    ftp.cwd('/main_directory/')

    filename = 'testfile.bin'

    with open(filename, 'wb') as localfile:
        ftp.retrbinary('RETR ' + filename, localfile.write, 1024)

    ftp.quit()
    localfile.close()

It just downloads the file and doesn't change the text label at all. Do I have to use QThread here? I also tried using asyncio but awaiting self.updateStatusText.setText("Connecting...") seems to return None and I get TypeError...

Answer 1

The following code should do:

class DownloadThread(QtCore.QThread):

    data_downloaded = QtCore.pyqtSignal(object)

    def run(self):
        self.data_downloaded.emit('Connecting...')

        ftp = FTP('example.com')
        ftp.login(user='user', passwd='password')

        ftp.cwd('/main_directory/')

        self.data_downloaded.emit('Downloading...')

        filename = 'testfile.bin'
        with open(filename, 'wb') as localfile:
            ftp.retrbinary('RETR ' + filename, localfile.write)

        ftp.quit()

        self.data_downloaded.emit('Done')

class MainWindow(QtGui.QWidget):
    def __init__(self):
        super(MainWindow, self).__init__()
        self.label = QtGui.QLabel
        self.button = QtGui.QPushButton("Start")
        self.button.clicked.connect(self.start_download)
        layout = QtGui.QVBoxLayout()
        layout.addWidget(self.button)
        layout.addWidget(self.label)
        self.setLayout(layout)

    def start_download(self):
        self.thread = DownloadThread()
        self.thread.data_downloaded.connect(self.on_data_ready)
        self.thread.start()

    def on_data_ready(self, data):
        self.label.setText(unicode(data))

Based on: Updating GUI elements in MultiThreaded PyQT.

Your followup question: Update PyQt progress from another thread running FTP download