如何在pyqt4中将行编辑中输入的所有文本显示为文本编辑小工具

from PyQt4 import QtGui, QtCore

class TextEditor(QtGui.QMainWindow):
    def __init__(self):
        super(TextEditor, self).__init__()
        self.initUI()

    def initUI(self):
        self.setWindowTitle("Text Editor")
        self.setGeometry(100, 100, 800, 600)

        self.text_edit = QtGui.QTextEdit(self)
        self.setCentralWidget(self.text_edit)

        self.statusBar()

        self.show()

    def update_text(self):
        text = self.line_edit.text()
        self.text_edit.setPlainText(text)

        self.line_edit = QtGui.QLineEdit(self)
        self.line_edit.returnPressed.connect(self.update_text)

        self.button = QtGui.QPushButton("Update", self)
        self.button.clicked.connect(self.update_text)

        layout = QtGui.QHBoxLayout()
        layout.addWidget(self.line_edit)
        layout.addWidget(self.button)

        widget = QtGui.QWidget(self)
        widget.setLayout(layout)
        self.setCentralWidget(widget)

if __name__ == '__main__':
    app = QtGui.QApplication(sys.argv)
    editor = TextEditor()
    sys.exit(app.exec_())