如何将日志输出重定向到PyQt文本小部件

Question

在一个关于 在PyQt中重定向输出 的帖子中，有段代码同时做了两件好事：它利用了 logging 模块来格式化消息，并且把标准的 stdout 和 stderr 输出重定向到了QT的 QTextBrowser 组件中。
但我希望 QTextBrowser 能接收到所有运行代码时的打印输出。特别是我想把来自日志记录器的格式化消息也重定向过去。
理想的解决方案是把每个日志记录器的输出都重定向到 QTextBrowser 中（而不仅仅是 stdout 和 stderr）。事实上，如果让我在这两者之间选择，我更愿意重定向日志记录器的消息，而不是 stdout 和 stderr 的输出……
所以这里是用来打印格式化消息的命令：

logger.debug('debug message')
logger.info('info message')
logger.warning('warning message')
logger.error('error message')

这是代码：

========

import sys
from PyQt4 import QtCore, QtGui
import logging
logger = logging.getLogger(__name__)

class XStream(QtCore.QObject):
    _stdout = None
    _stderr = None
    messageWritten = QtCore.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(QtGui.QDialog):
    def __init__( self, parent = None ):
        super(MyDialog, self).__init__(parent)

        self._console = QtGui.QTextBrowser(self)
        self._button  = QtGui.QPushButton(self)
        self._button.setText('Test Me')

        layout = QtGui.QVBoxLayout()
        layout.addWidget(self._console)
        layout.addWidget(self._button)
        self.setLayout(layout)

        XStream.stdout().messageWritten.connect( self._console.insertPlainText )
        XStream.stderr().messageWritten.connect( self._console.insertPlainText )

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

    def test( self ):
        print 'printing LINE 1'
        print 'printing LINE 2'
        logger.debug('debug message')
        logger.info('info message')
        logger.warning('warning message')
        logger.error('error message')
        # error out something
        print blah

if ( __name__ == '__main__' ):
    # logging.basicConfig()
    # logging.basicConfig(filename='example.log',level=logging.DEBUG)
    logging.basicConfig(level=logging.DEBUG)

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

    dlg = MyDialog()
    dlg.show()

    if ( app ):
        app.exec_()

后续发布::完整工作示例::由Mr.Dano解决

import sys
from PyQt4 import QtCore, QtGui
import logging

class QtHandler(logging.Handler):
    def __init__(self):
        logging.Handler.__init__(self)
    def emit(self, record):
        record = self.format(record)
        if record: XStream.stdout().write('%s\n'%record)
        # originally: XStream.stdout().write("{}\n".format(record))


logger = logging.getLogger(__name__)
handler = QtHandler()
handler.setFormatter(logging.Formatter("%(levelname)s: %(message)s"))
logger.addHandler(handler)
logger.setLevel(logging.DEBUG)


class XStream(QtCore.QObject):
    _stdout = None
    _stderr = None
    messageWritten = QtCore.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(QtGui.QDialog):
    def __init__( self, parent = None ):
        super(MyDialog, self).__init__(parent)

        self._console = QtGui.QTextBrowser(self)
        self._button  = QtGui.QPushButton(self)
        self._button.setText('Test Me')

        layout = QtGui.QVBoxLayout()
        layout.addWidget(self._console)
        layout.addWidget(self._button)
        self.setLayout(layout)

        XStream.stdout().messageWritten.connect( self._console.insertPlainText )
        XStream.stderr().messageWritten.connect( self._console.insertPlainText )

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

    def test( self ):
        logger.debug('debug message')
        logger.info('info message')
        logger.warning('warning message')
        logger.error('error message')
        print 'Old school hand made print message'

if ( __name__ == '__main__' ):
    app = None
    if ( not QtGui.QApplication.instance() ):
        app = QtGui.QApplication([])
    dlg = MyDialog()
    dlg.show()
    if ( app ):
        app.exec_()

Answer 1

dano给出的答案在2.7.x版本上有效，但在3.x版本上就不行了。

为了让@dano提供的代码在3.4.3版本上正常工作，我不得不对打印语句做一些明显的修改，还把XStream类中的write()方法从self.messageWritten.emit(unicode(msg))改成了self.messageWritten.emit(msg)。那个unicode调用让我觉得对话框就像在看着我笑一样，一动不动。

Answer 2

你可以创建一个自定义的 logging.Handler，然后把它添加到你的 logger 中：

import logging
logger = logging.getLogger(__name__)

class QtHandler(logging.Handler):

    def __init__(self):
        logging.Handler.__init__(self)

    def emit(self, record):
        record = self.format(record)
        XStream.stdout().write("{}\n".format(record))

handler = QtHandler()
handler.setFormatter(logging.Formatter("%(levelname)s: %(message)s"))
logger.addHandler(handler)
logger.setLevel(logging.DEBUG)

接着，在 if __name__ == "__main__": 这个块里，去掉 logging.basisConfig(level=logging.DEBUG) 这一行。这样你就只会在对话框里看到你的日志信息。