Use of QProcess to run and monitor system processes with PyQt

Question

I need a non blocking GUI solution to run an undefined number of system commands (like a bash script that takes some parameters as input), monitor their status. (e.g.: running/finished) and terminate (kill) the process.

An example can be:

1. choose an application from a list (QComboBox)

2. set a parameter (QLineEdit)

3. run it (QProcess)

AS it runs, append:

• command
• parameters
• Status

as row in a QTableWidget

.. I'm looking for a solution to monitor the status of each command.

The application can be a simple script like this one:

class runcommands(QWidget):
    def __init__(self, parent=None):
        super(runcommands, self).__init__(parent)

        layout = QFormLayout()
        self.commandlist = QComboBox()
        self.param = QLineEdit()
        self.runit = QToolButton()
        self.runit.setText('run')
        self.runit.clicked.connect(self.runcommand)
        self.commandlist.addItems(['simplerun.py', 'simplerun2.py'])
        self.table = QTableWidget()
        self.table.setColumnCount(5)
        self.model = QStandardItemModel()
        self.table.setHorizontalHeaderLabels(['Process', 'Parameter', 'STDOut', 'Status', 'Kill'])
        self.rowcount = 0

        layout.addRow(self.commandlist)
        layout.addRow(self.param)
        layout.addRow(self.runit)

        layout.addRow(self.table)

        self.setLayout(layout)
        self.setWindowTitle("Run & Monitor")
        self.commandrunning=0
        self.mylistofprocesses=[]



    def runcommand(self):
        # add a record in the QTableWidget
        # updating its row number at each run
        self.rowcount = self.rowcount + 1
        self.table.setRowCount(self.rowcount)

        # add column 0: command string
        self.c1 = QTableWidgetItem()
        self.c1.setText("%s" % os.path.join(os.getcwd(), self.commandlist.currentText()))
        self.table.setItem(self.rowcount - 1, 0, self.c1)

        # add column 1: parameter string
        self.c2 = QTableWidgetItem()
        self.c2.setText("%s" % self.param.text())
        self.table.setItem(self.rowcount - 1, 1, self.c2)

        # add column 2 to store the  Process StandardOutput
        stdout_item = QTableWidgetItem()
        self.table.setItem(self.rowcount - 1, 2, stdout_item)

        # add column 3: index to store the process status (0: Not Running, 1: Starting, 2: Running)
        status_item = QTableWidgetItem()
        self.table.setItem(self.rowcount - 1, 3, status_item)

        # add column 4: kill button to kill the relative process
        killbtn = QPushButton(self.table)
        killbtn.setText('Kill')
        self.table.setCellWidget(self.rowcount - 1, 4, killbtn)

        # Initiate a QProcess running a system command
        process = QtCore.QProcess()
        command = 'python3' + ' ' + os.getcwd() + '/' + self.commandlist.currentText() + ' ' + self.param.text()
        process.setProcessChannelMode(QtCore.QProcess.MergedChannels)
        # connect the stdout_item to the Process StandardOutput
        # it gets constantly update as the process emit std output
        process.readyReadStandardOutput.connect(lambda: stdout_item.setText(str(process.readAllStandardOutput().data().decode('utf-8'))))
        # start the process
        process.start(command)
        # this was supposed to add the process status in the relative column ... BUT it DOESN'T do it
        status_item.setText(str(process.ProcessState()))
        # connect the kill button to the process.kill method, to stop the process
        killbtn.clicked.connect(process.kill)
        killbtn.clicked.connect(lambda: killbtn.setText('Killed'))
        # this was supposed to 'UPDATE' the process status (from running to stoppted) in the relative column ... BUT it DOESN'T do it
        killbtn.clicked.connect(lambda: status_item.setText(str(process.ProcessState())))
        # append the process to a list so that it doesn't get destroyed at each run
        self.mylistofprocesses.append(process)


def main():
    app = QApplication(sys.argv)
    ex = runcommands()
    ex.show()
    sys.exit(app.exec_())


if __name__ == '__main__':
    main()

Thanks to help from Avaris on IRC I fixed the main issue of connecting each row in the table to a separate process.

After some editing to the original question, I've cleaned a little bit the code and I've been able to add the a button to stop/kill a process.

To complete this example task I need to implement the monitoring of all the active processes and update their status "in realtime" in the table at the 4th column (in addition of printing the std-output 3rd column).

I tried to do this with:

status_item.setText(str(process.ProcessState())))

but I can't get it to work.

Answer 1

You must use the stateChanged signal:

[...]
self.mylistofprocesses.append(process)

        status = {QProcess.NotRunning: "Not Running",
                  QProcess.Starting: "Starting",
                  QProcess.Running: "Running"}

        process.stateChanged.connect(lambda state: status_item.setText(status[state]))

Screenshots: