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I'm trying to update a PyQt4 progress bar live from an external python script as that external script runs through its loops. I've provided a minimal, working example of my progress so far; can anyone please guide me on best practices going forward?

GUI.py:

import sys, os

from pyface.qt import QtGui, QtCore

os.environ['ETS_TOOLKIT'] = 'qt4'

from traits.api import HasTraits,Instance,on_trait_change,Int

from traitsui.api import View,Item,VGroup

import external

#from PyQt4.QtCore import QThread





class P1(QtGui.QWidget):

    def __init__(self, parent=None):

        super(P1, self).__init__(parent)

        layout = QtGui.QGridLayout(self)



        def setProgress():

            if P1.progress.value() == 0:

                self.button.setDisabled(True)

                self.button.setText('Computing Data')



            external.op()



            if P1.progress.value() == 100:

                self.button_dist.setText('Data Complete')



        self.button = QtGui.QPushButton('Compute Data', self)

        self.connect(self.button, QtCore.SIGNAL('clicked()'), setProgress)

        layout.addWidget(self.button, 1, 2, 1, 1)

        self.button.setDisabled(False)

        self.button.show()



        P1.progress = QtGui.QProgressBar(self)

        P1.progress.setMinimum = 0

        P1.progress.setMaximum = 100

        P1.progress.setValue(0)        

        layout.addWidget(P1.progress, 1, 3, 1, 3)

        P1.progress.show()



class MainWindow(QtGui.QMainWindow):

    def __init__(self, parent=None):

        super(MainWindow, self).__init__(parent)

        self.window = P1(self) 

        self.setCentralWidget(self.window)

        self.show()



if __name__ == '__main__':

    app = QtGui.QApplication.instance()

    w = MainWindow()

    sys.exit(app.exec_())

external.py:

import sys, os, time

from pyface.qt import QtGui, QtCore

os.environ['ETS_TOOLKIT'] = 'qt4'

from GUI import P1

#from PyQt4.QtCore import QThread





def op():

    for i in range(1, 101):

        p1 = P1()

        p1.progress.setValue(i)

        time.sleep(0.01)

        print(i)

For this example to work as I intend, when you click the button Compute Data, the progress bar should fill in at the same rate that i in range(1,101) is printed in terminal.

You have a circular import that causes an infinite loop since GUI imports to external and external to GUI, that is a symptom of a bad design. On the other hand the progressbar must be a member of the class. In addition, the external task must be executed in a thread and to update them you must use a signal that will transport the data to the GUI thread.

external.py

import sys, os, time

from pyface.qt import QtGui, QtCore

os.environ['ETS_TOOLKIT'] = 'qt4'



def op(progress):

    for i in range(1, 101):

        progress.emit(i)

        time.sleep(0.01)

        print(i)

GUI.py

import sys, os

from pyface.qt import QtGui, QtCore

os.environ['ETS_TOOLKIT'] = 'qt4'

import threading

# from traits.api import HasTraits,Instance,on_trait_change,Int

# from traitsui.api import View,Item,VGroup

import external





class P1(QtGui.QWidget):

    progressChanged = QtCore.Signal(int)



    def __init__(self, parent=None):

        super(P1, self).__init__(parent)

        self.button = QtGui.QPushButton('Compute Data')

        self.button.clicked.connect(self.start_task)

        self.progress = QtGui.QProgressBar(minimum=0, maximum=100, value=0)

        self.progressChanged.connect(self.on_progressChanged) 



        layout = QtGui.QGridLayout(self)

        layout.addWidget(self.button, 1, 2, 1, 1)    

        layout.addWidget(self.progress, 1, 3, 1, 3)



    @QtCore.Slot()

    def start_task(self):

        t = threading.Thread(target=external.op, args=(self.progressChanged, ), daemon=True)

        t.start()



    @QtCore.Slot(int)

    def on_progressChanged(self, val):

        self.progress.setValue(val)

        if val == self.progress.maximum():

            self.button.setDisabled(False)

            self.button.setText('Data Complete')

        else:

            self.button.setText('Computing Data')

            self.button.setDisabled(True)



class MainWindow(QtGui.QMainWindow):

    def __init__(self, parent=None):

        super(MainWindow, self).__init__(parent)

        self.window = P1() 

        self.setCentralWidget(self.window)

        self.show()



if __name__ == '__main__':

    app = QtGui.QApplication.instance()

    if app is None:

        app = QtGui.QApplication()

    w = MainWindow()

    sys.exit(app.exec_())