短语高亮显示QEditText PyQt4 Python3

from PyQt4.QtGui import *
from PyQt4.QtCore import *

class Highlighter(QSyntaxHighlighter):
    def __init__(self, parent):
        super(Highlighter, self).__init__(parent)
        
        self.highlightingRules = []
        
        # 添加高亮规则
        rule = QTextCharFormat()
        rule.setForeground(Qt.red)
        rule.setFontWeight(QFont.Bold)
        pattern = QRegExp("QEditText")
        self.highlightingRules.append((pattern, rule))
        
    def highlightBlock(self, text):
        for pattern, rule in self.highlightingRules:
            expression = QRegExp(pattern)
            index = expression.indexIn(text)
            while index >= 0:
                length = expression.matchedLength()
                self.setFormat(index, length, rule)
                index = expression.indexIn(text, index + length)

class MainWindow(QMainWindow):
    def __init__(self):
        super(MainWindow, self).__init__()
        
        self.textEdit = QTextEdit()
        self.setCentralWidget(self.textEdit)
        
        highlighter = Highlighter(self.textEdit.document())
        
if __name__ == '__main__':
    import sys
    app = QApplication(sys.argv)
    mainWindow = MainWindow()
    mainWindow.show()
    sys.exit(app.exec_())