Redirecting Output in PyQt

Question

I have a QApplication, with a lot of classes and functions, which displays a lot of stdout on the console. I want to redirect this stdout and stderr to a QTextBrowser(this is also part of the QApplication). Is there any tweak to do this.

Answer 1

I have made a library of open-source PyQt custom widgets - one of which is a logger class (XLoggerWidget) and another of which is a full Python interpreter (XConsoleEdit). It does what you're looking for.

You can get it here if you want: http://dev.projexsoftware.com/projects/projexui

The part you're looking for is in the XConsoleEdit (projexui.widgets.xconsoleedit), but the general gist of it is:

import logging
import sys

from PyQt4.QtCore import QObject,\
                         pyqtSignal

from PyQt4.QtGui import QDialog, \
                        QVBoxLayout, \
                        QPushButton, \
                        QTextBrowser,\
                        QApplication

logger = logging.getLogger(__name__)

class XStream(QObject):
    _stdout = None
    _stderr = None

    messageWritten = pyqtSignal(str)

    def flush( self ):
        pass

    def fileno( self ):
        return -1

    def write( self, msg ):
        if ( not self.signalsBlocked() ):
            self.messageWritten.emit(unicode(msg))

    @staticmethod
    def stdout():
        if ( not XStream._stdout ):
            XStream._stdout = XStream()
            sys.stdout = XStream._stdout
        return XStream._stdout

    @staticmethod
    def stderr():
        if ( not XStream._stderr ):
            XStream._stderr = XStream()
            sys.stderr = XStream._stderr
        return XStream._stderr

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

        # setup the ui
        self._console = QTextBrowser(self)
        self._button  = QPushButton(self)
        self._button.setText('Test Me')

        # create the layout
        layout = QVBoxLayout()
        layout.addWidget(self._console)
        layout.addWidget(self._button)
        self.setLayout(layout)

        # create connections
        XStream.stdout().messageWritten.connect( self._console.insertPlainText )
        XStream.stderr().messageWritten.connect( self._console.insertPlainText )

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

    def test( self ):
        # print some stuff
        print 'testing'
        print 'testing2'

        # log some stuff
        logger.debug('Testing debug')
        logger.info('Testing info')
        logger.warning('Testing warning')
        logger.error('Testing error')

        # error out something
        print blah

if ( __name__ == '__main__' ):
    logging.basicConfig()

    app = None
    if ( not QApplication.instance() ):
        app = QApplication([])

    dlg = MyDialog()
    dlg.show()

    if ( app ):
        app.exec_()

This is a simplified version of whats in the XConsoleEdit, but its the general idea and should still work for what you're going for if you don't want to download the code.

In this example tho, you'll notice that only the print and error logs are routed through to the edit. If you want to connect the Python logging system to the edit, you'll need something a little more complex where you define a logging.Handler and link it to your widget.

That code would be found in projexui.widgets.xloggerwidget

Its a bit longer and more complex, so I'm not going to load it up here...but if you have any questions about it, let me know.