Best way to display logs in pyqt?

Question

I am currently working on a GUI using qt designer. I am wondering how I should go about printing strings on the GUI that acts like a logger window. I am using pyqt5.

Answer 1

Alex's answer should be ok in a single thread scenario, but if you are logging in another thread (QThread) you may get the following warning:

QObject::connect: Cannot queue arguments of type 'QTextCursor'
(Make sure 'QTextCursor' is registered using qRegisterMetaType().)

This is because you are modifying the GUI (self.widget.appendPlainText(msg)) from a thread other than the main thread without using the Qt Signal/Slot mechanism.

Here is my solution:

# my_logger.py

import logging
from PyQt5.QtCore import pyqtSignal, QObject

class Handler(QObject, logging.Handler):
    new_record = pyqtSignal(object)

    def __init__(self, parent):
        super().__init__(parent)
        super(logging.Handler).__init__()
        formatter = Formatter('%(asctime)s|%(levelname)s|%(message)s|', '%d/%m/%Y %H:%M:%S')
        self.setFormatter(formatter)

    def emit(self, record):
        msg = self.format(record)
        self.new_record.emit(msg) # <---- emit signal here

class Formatter(logging.Formatter):
    def formatException(self, ei):
        result = super(Formatter, self).formatException(ei)
        return result

    def format(self, record):
        s = super(Formatter, self).format(record)
        if record.exc_text:
            s = s.replace('\n', '')
        return s

   # gui.py

   ... # GUI code
   ...
   def setup_logger(self)
        handler = Handler(self)
        log_text_box = QPlainTextEdit(self)
        self.main_layout.addWidget(log_text_box)
        logging.getLogger().addHandler(handler)
        logging.getLogger().setLevel(logging.INFO)
        handler.new_record.connect(log_text_box.appendPlainText) # <---- connect QPlainTextEdit.appendPlainText slot
   ...