How can I use a QTextBrowser instead of the console in Python?

Question

I've constructed a window in PyQt 5, which by clicking on the "optimize" button, the program reads the "Gurobi-model.lp" file (click here to get the file), and optimizes it by the help of the Gurobi software. How can I display the logs of the Gurobi on a QTextBrowser?

I found some functions in the Gurobi such as OutputFlag, LogFile, and LogToConsole. Might these functions be helpful not?

For those who are not familiar with Gurobi, the Gurobi optimizer uses Python as an interface, and produces some logs that allows you to track the progress of the optimization. These logs are printed in the console during the optimization, and somehow, responding my question doesn't need to know anything about the Gurobi.

In the below code, I've found a way to show the logs in the QTextBrowser, but the logs are represented when the optimization process is completely done. I want the logs to be represented exactly during the optimization process.

import sys
from PyQt5.QtWidgets import *
from gurobipy import *
from io import *


class MyWindow(QWidget):

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

        self.pb = QPushButton(self.tr("optimize"))
        self.log_text = QTextBrowser()

        layout = QVBoxLayout(self)
        layout.addWidget(self.pb)
        layout.addWidget(self.log_text)
        self.setLayout(layout)

        self.pb.clicked.connect(self.optimize)

     def optimize(self):

        f = StringIO()
        sys.stdout = StringIO()

        self.m = read('Gurobi-model.lp')
        self.m.optimize()
        self.log_text.append(sys.stdout.getvalue() )


def main():
   app = QApplication(sys.argv)
   w = MyWindow()
   w.show()
   sys.exit(app.exec_())

if __name__ == "__main__":
    main()

Answer 1

The task of optimizing is heavy, so it should not be executed in the same thread of the GUI, nor in the same process. For this you should use the multiprocessing module. On the other hand, if you need to show the output of the console in the QTextBrowser, you must use the logging module, passing it through signal (for the last part, use the answer of this post).

import sys
import logging
import multiprocessing
from logging.handlers import QueueHandler, QueueListener
from PyQt5 import QtCore, QtWidgets
from gurobipy import *

class LogEmitter(QtCore.QObject):
    sigLog = QtCore.pyqtSignal(str)

class LogHandler(logging.Handler):
    def __init__(self):
        super().__init__()
        self.emitter = LogEmitter()

    def emit(self, record):
        msg = self.format(record)
        self.emitter.sigLog.emit(msg)

def long_task():
    m = read('Gurobi-model.lp')
    m.optimize()

def worker_init(q):
    qh = QueueHandler(q)
    logger = logging.getLogger()
    logger.setLevel(logging.INFO)
    logger.addHandler(qh)

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

        self.pb = QtWidgets.QPushButton(self.tr("optimize"),
            clicked=self.start_optimize)
        self.log_text = QtWidgets.QPlainTextEdit(readOnly=True)

        layout = QtWidgets.QVBoxLayout(self)
        layout.addWidget(self.pb)
        layout.addWidget(self.log_text)

        self.running = False
        handler = LogHandler()
        handler.emitter.sigLog.connect(self.log_text.appendPlainText)

        self.q = multiprocessing.Queue()
        self.ql = QueueListener(self.q, handler)
        self.ql.start()

        self.main_log = logging.getLogger('main')
        self.main_log.propagate = False
        self.main_log.setLevel(logging.INFO)
        self.main_log.addHandler(QueueHandler(self.q))
        self.pool = multiprocessing.Pool(1, worker_init, [self.q])

    @QtCore.pyqtSlot()
    def start_optimize(self):
        if not self.running:
            self.pool.apply_async(long_task, callback=self.handle_result)

    def handle_result(self, result=None):
        self.running = False

    def closeEvent(self, event):
        self.ql.stop()
        super(MyWindow, self).closeEvent(event)

def main():
   app = QtWidgets.QApplication(sys.argv)
   w = MyWindow()
   w.show()
   sys.exit(app.exec_())

if __name__ == "__main__":
    main()