Redirecting Logging of a Different File to QPlainTextEdit

Question

My PyQt5 application is a GUI that runs a python script, another_module.py, within a QProcess. another_module.py has a logging mechanism that writes to stdout. I would like to be able to connect the logging in another_module.py and redirect it to a text box in the GUI such that whatever logging another_module.py generates be printed/appended to the text box in my GUI. My code is in below.

my_gui.py

import sys
from PyQt5 import QtWidgets
from PyQt5.QtCore import QProcess
import logging
import another_module # This file has a sample logging mechanism which I would like to have access in my_gui.py

logging.basicConfig(level=logging.DEBUG, format=' %(asctime)s - %(name)s - %(levelname)s - %(message)s')

class QTextEditLogger(logging.Handler):
    def __init__(self, parent):
        super().__init__()
        self.widget = QtWidgets.QPlainTextEdit(parent)
        self.widget.setReadOnly(True)

    def emit(self, record):
        msg = self.format(record)
        self.widget.appendPlainText(msg)


class MyDialog(QtWidgets.QDialog, QtWidgets.QPlainTextEdit):
    def __init__(self, parent=None):
        super().__init__(parent)

        # Setup logging here:
        logTextBox = QTextEditLogger(self)
        logTextBox.setFormatter(logging.Formatter('%(asctime)s - %(levelname)s - %(message)s'))
        logging.getLogger().addHandler(logTextBox) # root logging nicely redirects to logTextBox 
        logging.getLogger().setLevel(logging.DEBUG)
        another_module.logger.addHandler(logTextBox) # logging of the other file is not redirected to logTextBox
        another_module.logger.setLevel(logging.DEBUG)

        self.process = None
        self._button = QtWidgets.QPushButton(self)
        self._button.setText('Start')

        layout = QtWidgets.QVBoxLayout()
        layout.addWidget(logTextBox.widget)
        layout.addWidget(self._button)
        self.setLayout(layout)

        self._button.clicked.connect(self.test)

    def test(self):
        logging.debug('damn, a bug')
        logging.info('something to remember')
        logging.warning('that\'s not right')
        logging.error('foobar')

        self.process = QProcess(self)
        self.process.started.connect(lambda: print('Started!'))
        self.process.finished.connect(lambda: print('Finished!'))
        self.process.startDetached('python another_module.py')


app = QtWidgets.QApplication(sys.argv)
dlg = MyDialog()
dlg.show()
dlg.raise_()
sys.exit(app.exec_())

another_module.py

import logging
import sys
import time

logger = logging.getLogger(__name__)
logger.setLevel(logging.INFO)
formatter = logging.Formatter('%(asctime)s:%(name)s:%(funcName)s:%(lineno)d:%(message)s')
file_handler = logging.FileHandler('another_module.log')
file_handler.setLevel(logging.INFO)
file_handler.setFormatter(formatter)
stream_handler = logging.StreamHandler(sys.stdout)
stream_handler.setFormatter(formatter)
logger.addHandler(file_handler)
logger.addHandler(stream_handler)

def create_some_log():
    while True:
        logger.debug('<<different file>> damn, a bug')
        logger.info('<<different file>> something to remember')
        logger.warning('<<different file>> that\'s not right')
        logger.error('<<different file>> foobar')
        time.sleep(5)

if __name__ == '__main__':
    create_some_log()

How can I redirect the output of the logging inside another_module.py to the textbox in my_gui.py?

My code above runs with no problem and the console prints the following information:

 2020-10-04 22:39:23,975 - root - DEBUG - damn, a bug
 2020-10-04 22:39:23,976 - root - INFO - something to remember
 2020-10-04 22:39:23,976 - root - WARNING - that's not right
 2020-10-04 22:39:23,976 - root - ERROR - foobar
2020-10-04 22:49:27,457:__main__:create_some_log:22:<<different file>> something to remember
2020-10-04 22:49:27,457:__main__:create_some_log:23:<<different file>> that's not right
2020-10-04 22:49:27,457:__main__:create_some_log:24:<<different file>> foobar

However, only the root logging is printed to the text box in the gui:

 2020-10-04 22:39:23,975 - root - DEBUG - damn, a bug
 2020-10-04 22:39:23,976 - root - INFO - something to remember
 2020-10-04 22:39:23,976 - root - WARNING - that's not right
 2020-10-04 22:39:23,976 - root - ERROR - foobar

Answer 1

If you are going to run the script with QProcess then it will run in a different process so doing another_module.logger.addHandler(logTextBox) and another_module.logger.setLevel(logging.DEBUG) will not modify anything or make sense. The idea in this case is to get the log using the readAllStandardOutput() method:

import logging
import os
import sys

from PyQt5 import QtCore, QtWidgets


CURRENT_DIR = os.path.dirname(os.path.realpath(__file__))
logging.basicConfig(
    level=logging.DEBUG, format=" %(asctime)s - %(name)s - %(levelname)s - %(message)s"
)


class QTextEditLogger(logging.Handler):
    def __init__(self, parent):
        super().__init__()
        self.widget = QtWidgets.QPlainTextEdit(parent)
        self.widget.setReadOnly(True)

    def emit(self, record):
        msg = self.format(record)
        self.widget.appendPlainText(msg)


class MyDialog(QtWidgets.QDialog):
    def __init__(self, parent=None):
        super().__init__(parent)

        # Setup logging here:
        self.logTextBox = QTextEditLogger(self)
        self.logTextBox.setFormatter(
            logging.Formatter("%(asctime)s - %(levelname)s - %(message)s")
        )
        logging.getLogger().addHandler(self.logTextBox)
        logging.getLogger().setLevel(logging.DEBUG)

        self._button = QtWidgets.QPushButton()
        self._button.setText("Start")

        layout = QtWidgets.QVBoxLayout(self)
        layout.addWidget(self.logTextBox.widget)
        layout.addWidget(self._button)

        self._button.clicked.connect(self.test)

        self.process = QtCore.QProcess()
        self.process.readyReadStandardOutput.connect(
            self.handle_readyReadStandardOutput
        )
        self.process.started.connect(lambda: print("Started!"))
        self.process.finished.connect(lambda: print("Finished!"))

    def test(self):
        logging.debug("damn, a bug")
        logging.info("something to remember")
        logging.warning("that's not right")
        logging.error("foobar")

        script = os.path.join(CURRENT_DIR, "another_module.py")
        self.process.start(sys.executable, [script])

    def handle_readyReadStandardOutput(self):
        text = self.process.readAllStandardOutput().data().decode()
        self.logTextBox.widget.appendPlainText(text.strip())


if __name__ == "__main__":
    app = QtWidgets.QApplication(sys.argv)
    dlg = MyDialog()
    dlg.show()
    dlg.raise_()
    sys.exit(app.exec_())