打印行按按钮编辑文本

当按下“OK”(确定)按钮时,如何更改以下代码,使其打印在line edit widget中写入的内容?当前版本返回“Example”对象没有属性textbox”错误。

import sys
from PyQt5.QtWidgets import QApplication, QWidget,QPushButton,QLineEdit, QHBoxLayout, QLabel, QVBoxLayout
from PyQt5.QtGui import QIcon


class Example(QWidget):

    def __init__(self):
        super().__init__()

        self.initUI()


    def initUI(self):

        label = QLabel('Keyword') 
        button = QPushButton('OK')
        textbox = QLineEdit()
        hbox = QHBoxLayout()
        hbox.addWidget(label)
        hbox.addWidget(textbox)
        hbox.addWidget(button)

        vbox = QVBoxLayout()
        vbox.addLayout(hbox)
        vbox.addStretch(1)

        button.clicked.connect(self.button_clicked)

        self.setLayout(vbox)   

        self.setGeometry(300, 300, 300, 220)
        self.setWindowTitle('Icon')
        self.setWindowIcon(QIcon('web.png')) 
        self.show()

    def button_clicked(self):
        print(self.textbox.text())

if __name__ == '__main__':

    app = QApplication(sys.argv)
    ex = Example()
    sys.exit(app.exec_())

`