Question

I am trying to show the loop data in Lineedit but it is not updating. Even the print command does not print the data on the terminal till I press any key other than return in lineedit. Have a look at the program and suggest me the changes:

import sys
import time
from PyQt4.QtGui import *
from PyQt4.QtCore import *

class MyFrame(QWidget):
def __init__(self):
    QWidget.__init__(self)

    self.le = QLineEdit(self)
    self.le.setGeometry(200,200,75,35)

    i=0
    self.le.setText(str(i))

    self.connect(self.le, SIGNAL("textChanged(QString)"),self.updatedvalue)

def updatedvalue(self):

    for i in range(1,5):
        self.le.setText(str(i))
        print(i)
        time.sleep(1)

app=QApplication(sys.argv)
f=MyFrame()
f.show()
app.exec_()

Answer 1

You’ll need to call QApplication.instance.processEvents() after updating your QLineEdit‘s text to force an update, otherwise you won’t see anything until the final number.

You also need to change your textChanged() signal to textEdited(). Using textChanged() your updatedvalue() function will be called again on the first pass of your loop once setText() is called because you’re updating the QLineEdit‘s text. The textEdited() signal won’t be triggered if you update the text programmatically.

import sys
import time
from PyQt4.QtGui import *
from PyQt4.QtCore import *

class MyFrame(QWidget):
    def __init__(self):
        QWidget.__init__(self)

        self.le = QLineEdit(self)
        self.le.setGeometry(200,200,75,35)

        i = 0
        self.le.setText(str(i))

        self.connect(self.le, SIGNAL("textEdited(QString)"),self.updatedvalue)

    def updatedvalue(self):
        for i in range(1,5):
            self.le.setText(str(i))
            QApplication.instance().processEvents()
            print(i)
            time.sleep(1)

app=QApplication(sys.argv)
f=MyFrame()
f.show()
app.exec_()

As Bob mentioned, using a QTimer would be much better.