[FIXED] PyQt4: QProcess readyRead does not always emit correctly

Issue

When I use pyqt to run a program I cannot get the output correctly every time. Here is an example:

from PyQt4 import QtCore, QtGui
import sys


class MainWindow(QtGui.QMainWindow):
    def __init__(self):
        QtGui.QWidget.__init__(self)

        program = "ping"

        self.process = QtCore.QProcess()
        self.process.readyRead.connect(self.readoutput)
        self.process.start(program)

    def readoutput(self):
        print str(self.process.readAll())

def main():
    app = QtGui.QApplication(sys.argv)
    ex = MainWindow()
    sys.exit(app.exec_())

if __name__ == '__main__':
    main()

In this case, the output is the helper of the ping command, as I would expect. Although if I change the program variable to some other value it doesn't always work, for example if i do:

program = "pyinstaller"

it does not print the helper of pyinstaller as it happens in the console. How am I supposed to get the output in this case?

Solution

pyinstaller might be printing to stderr instead of stdout. You can cause QProcess.readAll() to return both outputs by calling (before self.process.start(program))

setProcessChannelMode(QProcess.MergedChannels)

Answered By - David Ching