Unable to get output of a Python script with qprocess

Question

I am trying to get the output of a Python script with qprocess but I can't seem to make it work. I think the issue is with the script since I can get the output of a test script I wrote without a problem. I don't know enough about python to see what the issue is. What might be the problem?

My C++ qt program:

#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent)
    : QMainWindow(parent)
    , ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}


void MainWindow::on_pushButton_clicked()
    {
       QString monitor = "/home/monitor-ofono.py";
   // QString monitor = "/home/test3.py";

            myprocess = new QProcess(this);
            connect(myprocess, SIGNAL(readyReadStandardOutput()),
                    this, SLOT(readOutput()));
            myprocess->setProcessChannelMode(QProcess::MergedChannels);
            myprocess->start(monitor);

            //myprocess->waitForFinished();
            qDebug() << "error code:" << myprocess->error();
    }

void MainWindow::readOutput()
{
    QString textOut = myprocess->readAllStandardOutput();
      emit myOutput(textOut);
    ui->textEdit->setText(textOut);
}

My test script that works

#!/usr/bin/env python3
# -*- coding: utf-8 -*-
"""
Created on Wed May  4 12:03:17 2022

@author: me
"""

import time
import sys

for i in range(5):
    print(i),
    sys.stdout.flush()
    time.sleep(1)

The script I am trying to get the output from returns nothing to qprocess but works fine in a terminal

#!/usr/bin/python3

from gi.repository import GLib

import dbus
import dbus.mainloop.glib

_dbus2py = {
    dbus.String : str,
    dbus.UInt32 : int,
    dbus.Int32 : int,
    dbus.Int16 : int,
    dbus.UInt16 : int,
    dbus.UInt64 : int,
    dbus.Int64 : int,
    dbus.Byte : int,
    dbus.Boolean : bool,
    dbus.ByteArray : str,
    dbus.ObjectPath : str
    }

def dbus2py(d):
    t = type(d)
    if t in _dbus2py:
        return _dbus2py[t](d)
    if t is dbus.Dictionary:
        return dict([(dbus2py(k), dbus2py(v)) for k, v in d.items()])
    if t is dbus.Array and d.signature == "y":
        return "".join([chr(b) for b in d])
    if t is dbus.Array or t is list:
        return [dbus2py(v) for v in d]
    if t is dbus.Struct or t is tuple:
        return tuple([dbus2py(v) for v in d])
    return d

def pretty(d):
    d = dbus2py(d)
    t = type(d)

    if t in (dict, tuple, list) and len(d) > 0:
        if t is dict:
            d = ", ".join(["%s = %s" % (k, pretty(v))
                    for k, v in d.items()])
            return "{ %s }" % d

        d = " ".join([pretty(e) for e in d])

        if t is tuple:
            return "( %s )" % d

    if t is str:
        return "%s" % d

    return str(d)

def property_changed(name, value, path, interface):
    iface = interface[interface.rfind(".") + 1:]
    print("{%s} [%s] %s = %s" % (iface, path, name, pretty(value)))

def added(name, value, member, path, interface):
    iface = interface[interface.rfind(".") + 1:]
    print("{%s} [%s] %s %s" % (iface, member, name, pretty(value)))

def removed(name, member, path, interface):
    iface = interface[interface.rfind(".") + 1:]
    print("{%s} [%s] %s" % (iface, name, member))

def event(member, path, interface):
    iface = interface[interface.rfind(".") + 1:]
    print("{%s} [%s] %s" % (iface, path, member))

def message(msg, args, member, path, interface):
    iface = interface[interface.rfind(".") + 1:]
    print("{%s} [%s] %s %s (%s)" % (iface, path, member,
                    msg, pretty(args)))

def ussd(msg, member, path, interface):
    iface = interface[interface.rfind(".") + 1:]
    print("{%s} [%s] %s %s" % (iface, path, member, msg))

def value(value, member, path, interface):
    iface = interface[interface.rfind(".") + 1:]
    print("{%s} [%s] %s %s" % (iface, path, member, str(value)))

if __name__ == '__main__':
    dbus.mainloop.glib.DBusGMainLoop(set_as_default=True)

    bus = dbus.SystemBus()

    bus.add_signal_receiver(property_changed,
                bus_name="org.ofono",
                signal_name = "PropertyChanged",
                path_keyword="path",
                interface_keyword="interface")

    for member in ["IncomingBarringInEffect",
            "OutgoingBarringInEffect",
            "NearMaximumWarning"]:
        bus.add_signal_receiver(event,
                    bus_name="org.ofono",
                    signal_name = member,
                    member_keyword="member",
                    path_keyword="path",
                    interface_keyword="interface")

    for member in ["ModemAdded",
            "ContextAdded",
            "CallAdded",
            "MessageAdded"]:
        bus.add_signal_receiver(added,
                    bus_name="org.ofono",
                    signal_name = member,
                    member_keyword="member",
                    path_keyword="path",
                    interface_keyword="interface")

    for member in ["ModemRemoved",
            "ContextRemoved",
            "CallRemoved",
            "MessageRemoved"]:
        bus.add_signal_receiver(removed,
                    bus_name="org.ofono",
                    signal_name = member,
                    member_keyword="member",
                    path_keyword="path",
                    interface_keyword="interface")

    for member in ["DisconnectReason", "Forwarded", "BarringActive"]:
        bus.add_signal_receiver(value,
                    bus_name="org.ofono",
                    signal_name = member,
                    member_keyword="member",
                    path_keyword="path",
                    interface_keyword="interface")

    for member in ["IncomingBroadcast", "EmergencyBroadcast",
            "IncomingMessage", "ImmediateMessage"]:
        bus.add_signal_receiver(message,
                    bus_name="org.ofono",
                    signal_name = member,
                    member_keyword="member",
                    path_keyword="path",
                    interface_keyword="interface")

    for member in ["NotificationReceived", "RequestReceived"]:
        bus.add_signal_receiver(ussd,
                    bus_name="org.ofono",
                    signal_name = member,
                    member_keyword="member",
                    path_keyword="path",
                    interface_keyword="interface")

    mainloop = GLib.MainLoop()
    mainloop.run()

Answer 1

Got it working by adding ,file=sys.stdout, flush=True to the print lines like below: print("{%s} [%s] %s" % (iface, path, member),file=sys.stdout, flush=True) Below is the complete python file with my edits.

#!/usr/bin/python3

from gi.repository import GLib

import dbus
import dbus.mainloop.glib
import sys

_dbus2py = {
    dbus.String : str,
    dbus.UInt32 : int,
    dbus.Int32 : int,
    dbus.Int16 : int,
    dbus.UInt16 : int,
    dbus.UInt64 : int,
    dbus.Int64 : int,
    dbus.Byte : int,
    dbus.Boolean : bool,
    dbus.ByteArray : str,
    dbus.ObjectPath : str
    }

def dbus2py(d):
    t = type(d)
    if t in _dbus2py:
        return _dbus2py[t](d)
    if t is dbus.Dictionary:
        return dict([(dbus2py(k), dbus2py(v)) for k, v in d.items()])
    if t is dbus.Array and d.signature == "y":
        return "".join([chr(b) for b in d])
    if t is dbus.Array or t is list:
        return [dbus2py(v) for v in d]
    if t is dbus.Struct or t is tuple:
        return tuple([dbus2py(v) for v in d])
    return d

def pretty(d):
    d = dbus2py(d)
    t = type(d)

    if t in (dict, tuple, list) and len(d) > 0:
        if t is dict:
            d = ", ".join(["%s = %s" % (k, pretty(v))
                    for k, v in d.items()])
            return "{ %s }" % d

        d = " ".join([pretty(e) for e in d])

        if t is tuple:
            return "( %s )" % d

    if t is str:
        return "%s" % d

    return str(d)

def property_changed(name, value, path, interface):
    iface = interface[interface.rfind(".") + 1:]
    print("{%s} [%s] %s = %s" % (iface, path, name, pretty(value)),file=sys.stdout, flush=True)


def added(name, value, member, path, interface):
    iface = interface[interface.rfind(".") + 1:]
    print("{%s} [%s] %s %s" % (iface, member, name, pretty(value)),file=sys.stdout, flush=True)


def removed(name, member, path, interface):
    iface = interface[interface.rfind(".") + 1:]
    print("{%s} [%s] %s" % (iface, name, member),file=sys.stdout, flush=True)


def event(member, path, interface):
    iface = interface[interface.rfind(".") + 1:]
    print("{%s} [%s] %s" % (iface, path, member),file=sys.stdout, flush=True)


def message(msg, args, member, path, interface):
    iface = interface[interface.rfind(".") + 1:]
    print("{%s} [%s] %s %s (%s)" % (iface, path, member,
                    msg, pretty(args)),file=sys.stdout, flush=True)


def ussd(msg, member, path, interface):
    iface = interface[interface.rfind(".") + 1:]
    print("{%s} [%s] %s %s" % (iface, path, member, msg),file=sys.stdout, flush=True)


def value(value, member, path, interface):
    iface = interface[interface.rfind(".") + 1:]
    print("{%s} [%s] %s %s" % (iface, path, member, str(value)),file=sys.stdout, flush=True)


if __name__ == '__main__':
    dbus.mainloop.glib.DBusGMainLoop(set_as_default=True)

    bus = dbus.SystemBus()

    bus.add_signal_receiver(property_changed,
                bus_name="org.ofono",
                signal_name = "PropertyChanged",
                path_keyword="path",
                interface_keyword="interface")

    for member in ["IncomingBarringInEffect",
            "OutgoingBarringInEffect",
            "NearMaximumWarning"]:
        bus.add_signal_receiver(event,
                    bus_name="org.ofono",
                    signal_name = member,
                    member_keyword="member",
                    path_keyword="path",
                    interface_keyword="interface")

    for member in ["ModemAdded",
            "ContextAdded",
            "CallAdded",
            "MessageAdded"]:
        bus.add_signal_receiver(added,
                    bus_name="org.ofono",
                    signal_name = member,
                    member_keyword="member",
                    path_keyword="path",
                    interface_keyword="interface")

    for member in ["ModemRemoved",
            "ContextRemoved",
            "CallRemoved",
            "MessageRemoved"]:
        bus.add_signal_receiver(removed,
                    bus_name="org.ofono",
                    signal_name = member,
                    member_keyword="member",
                    path_keyword="path",
                    interface_keyword="interface")

    for member in ["DisconnectReason", "Forwarded", "BarringActive"]:
        bus.add_signal_receiver(value,
                    bus_name="org.ofono",
                    signal_name = member,
                    member_keyword="member",
                    path_keyword="path",
                    interface_keyword="interface")

    for member in ["IncomingBroadcast", "EmergencyBroadcast",
            "IncomingMessage", "ImmediateMessage"]:
        bus.add_signal_receiver(message,
                    bus_name="org.ofono",
                    signal_name = member,
                    member_keyword="member",
                    path_keyword="path",
                    interface_keyword="interface")

    for member in ["NotificationReceived", "RequestReceived"]:
        bus.add_signal_receiver(ussd,
                    bus_name="org.ofono",
                    signal_name = member,
                    member_keyword="member",
                    path_keyword="path",
                    interface_keyword="interface")
    sys.stdout.flush()
    mainloop = GLib.MainLoop()
    mainloop.run()