Pyqt Gui Freezes while in loop

Question

Im making port scanner program with PyQt but Gui freezes when i activate loop.How can i fix that? I added time.sleep() function but it still freezes. This is the function it freezes. Thanks.

        try:
            time.sleep(1) 
            hostname=self.adres.text()
            hostip=socket.gethostbyname(hostname)
            uyari1="Scanning remote host, {}\n".format(hostip)
            self.durum.append(uyari1)
            print(uyari1)
            for port in range(1,1025):
                time.sleep(0.1)  
                sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
                result = sock.connect_ex((hostip, port))
                if result == 0:
                    time.sleep(0.01) 
                    print ("Port {}: \t Open".format(port))
                    self.durum.append("Port {}: \t Open\n".format(port))
                sock.close()

Full code:

import socket,os,time
from PyQt4 import QtCore, QtGui

try:
    _fromUtf8 = QtCore.QString.fromUtf8
except AttributeError:
    def _fromUtf8(s):
        return s

try:
    _encoding = QtGui.QApplication.UnicodeUTF8
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig, _encoding)
except AttributeError:
    def _translate(context, text, disambig):
        return QtGui.QApplication.translate(context, text, disambig)

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName(_fromUtf8("MainWindow"))
        MainWindow.resize(596, 412)
        self.centralwidget = QtGui.QWidget(MainWindow)
        self.centralwidget.setObjectName(_fromUtf8("centralwidget"))
        self.label = QtGui.QLabel(self.centralwidget)
        self.label.setGeometry(QtCore.QRect(120, -10, 331, 91))
        self.label.setObjectName(_fromUtf8("label"))
        self.label_2 = QtGui.QLabel(self.centralwidget)
        self.label_2.setGeometry(QtCore.QRect(10, 90, 91, 16))
        self.label_2.setObjectName(_fromUtf8("label_2"))
        self.adres = QtGui.QLineEdit(self.centralwidget)
        self.adres.setGeometry(QtCore.QRect(100, 90, 371, 22))
        self.adres.setObjectName(_fromUtf8("adres"))
        self.durum = QtGui.QTextEdit(self.centralwidget)
        self.durum.setGeometry(QtCore.QRect(10, 140, 571, 191))
        self.durum.setObjectName(_fromUtf8("durum"))
        self.baslat = QtGui.QPushButton(self.centralwidget)
        self.baslat.setGeometry(QtCore.QRect(480, 90, 101, 21))
        self.baslat.setObjectName(_fromUtf8("baslat"))
        self.dosyaya = QtGui.QPushButton(self.centralwidget)
        self.dosyaya.setGeometry(QtCore.QRect(490, 340, 91, 25))
        self.dosyaya.setObjectName(_fromUtf8("dosyaya"))
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtGui.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 596, 21))
        self.menubar.setObjectName(_fromUtf8("menubar"))
        MainWindow.setMenuBar(self.menubar)
        self.hakkindaa = QtGui.QPushButton(self.centralwidget)
        self.hakkindaa.setGeometry(QtCore.QRect(10, 340, 91, 25))
        self.hakkindaa.setObjectName(_fromUtf8("hakkindaa"))
        self.hakkindaa.setText("Hakkında")
        self.statusbar = QtGui.QStatusBar(MainWindow)
        self.statusbar.setObjectName(_fromUtf8("statusbar"))
        MainWindow.setStatusBar(self.statusbar)
        QtCore.QObject.connect(self.hakkindaa, QtCore.SIGNAL(_fromUtf8("clicked()")), self.hakkinda)
        QtCore.QObject.connect(self.dosyaya, QtCore.SIGNAL(_fromUtf8("clicked()")), self.dosyayaya)
        QtCore.QObject.connect(self.baslat, QtCore.SIGNAL(_fromUtf8("clicked()")), self.baslat_btn)
        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def hakkinda(self):
        QtGui.QMessageBox.about(None, "About", "Ege Öz 2014")

    def baslat_btn(self):
        try:
            time.sleep(1) 
            hostname=self.adres.text()
            hostip=socket.gethostbyname(hostname)
            uyari1="Scanning remote host, {}\n".format(hostip)
            self.durum.append(uyari1)
            print(uyari1)
            for port in range(1,1025):
                time.sleep(0.1)  
                sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
                result = sock.connect_ex((hostip, port))
                if result == 0:
                    time.sleep(0.01) 
                    print ("Port {}: \t Open".format(port))
                    self.durum.append("Port {}: \t Open\n".format(port))
                sock.close()

        except socket.gaierror:
            self.durum.append("Hostname could not be resolved.")
            print("Hostname could not be resolved.")
            self.adres.setText("")
        except socket.error:

            self.durum.append("Could not connect to server.")
            print("Could not connect to server.")
            self.adres.setText("")
    def dosyayaya(self):
            self.durum.append("Saving log file to home directory...")
            ev=os.getenv("USER")
            data=self.durum.toPlainText()
            yol="/home/"+ev+"/portscanner.log"
            f = open (yol,"w")
            f.write(data)
            f.close()
            self.durum.append("Log file saved.")
            print ("Log file saved.")
    def retranslateUi(self, MainWindow):
        MainWindow.setWindowTitle(_translate("MainWindow", "Port Scanner", None))
        self.label.setText(_translate("MainWindow", "<html><head/><body><p align=\"center\"><span style=\" font-size:11pt; font-weight:600;\">Port Scanner</span></p><p>Enter the remote host adress and press start.</p></body></html>", None))
        self.label_2.setText(_translate("MainWindow", "Remote Host:", None))
        self.baslat.setText(_translate("MainWindow", "Start Scanning", None))
        self.dosyaya.setText(_translate("MainWindow", "Save to file", None))    

if __name__ == "__main__":
    import sys
    app = QtGui.QApplication(sys.argv)
    MainWindow = QtGui.QMainWindow()
    ui = Ui_MainWindow()
    ui.setupUi(MainWindow)
    MainWindow.show()
    sys.exit(app.exec_())

Answer 1

You should call QtCore.QCoreApplication.processEvents() within your for loop to make the Qt's event loop proceed the incoming event (from keyboard or mouse).

Answer 2

Although calling QtCore.QCoreApplication.processEvents() works now, I have read in many places on the web that it should be a last resort. Unfortunately none of the sources clearly explain why -- but see for example

• How to make Qt work when main thread is busy?
• Should I use QCoreApplication::processEvents() or QApplication::processEvents()?
• How to implement a QThread that runs forever{} with a QWaitCondition but still needs to catch another Slot while doing that
• http://qt-project.org/forums/viewthread/22967

So it does seem allowed, but in general, it seems to be better design to use QTimer or QThread.