python + pyqt5 QlineEdit QMessageBox实现信息录入和消息弹框提醒

本人现在在做自动化工具开发的工作，因此，记录下自己平时遇到的问题和解决之道，还有一些简单的小工具

以下为主代码

# --*-- coding:utf-8 --*--

from first import Ui_MainWindow
from PyQt5.QtWidgets import QApplication, QMainWindow,QMessageBox
import os
import sys
reload(sys)
sys.setdefaultencoding('utf-8')

gcardnum = eval(sys.argv[1])

class Mainwindow(QMainWindow, Ui_MainWindow):
    global card_num
    def __init__(self):
        super(Mainwindow, self).__init__()
        self.setupUi(self)
        self.click_num = 1
        self.sn_list = []
        self.card_num = gcardnum
        self.label_2.setText(u"数量为:%s" % self.card_num)
        self.label.setText(u"第%s块" % self.click_num)
        self.button_OK.clicked.connect(self.begin_get)
        self.button_cancel.clicked.connect(self.cancel)

    def scan_sn(self, sn):
        if sn!="":
            with open("sn.txt", "a+") as fw:
                if len(sn) == 17:
                    if sn not in self.sn_list:
                        if self.click_num == int(self.card_num):
                            QMessageBox.information(self, '提示信息', '保存成功')
                            self.close()
                        self.sn_list.append(sn)
                        fw.write("%s\n" % sn)
                        self.lineEdit_sn.clear()
                        self.click_num += 1
                        self.label.setText(u"第%s块" % self.click_num)
                    else:
                        QMessageBox.information(self, '提示信息', '重复')
                        self.lineEdit_sn.clear()
                else:
                    QMessageBox.information(self, '提示信息', '输入有误')
                    self.lineEdit_sn.clear()
        else:
            QMessageBox.information(self, '提示信息', '不能为空')

    def keyPressEvent(self, event):
        sn = self.lineEdit_sn.text()
        if str(event.key()) == "":
            self.scan_sn(sn)

    def begin_get(self):
        sn = self.lineEdit_sn.text()
        self.scan_sn(sn)

    def cancel(self):
        self.lineEdit_sn.clear()

if __name__ == '__main__':
    if os.path.exists("sn.txt"):
        os.remove("sn.txt")
    app = QApplication(sys.argv)
    mainWindow = Mainwindow()
    mainWindow.show()
    sys.exit(app.exec_())

以下为pyqt界面设计

# -*- coding: utf-8 -*-

# Form implementation generated from reading ui file 'first.ui'
#
# Created: Wed Jul 18 14:57:14 2018
#      by: PyQt5 UI code generator 5.3.2
#
# WARNING! All changes made in this file will be lost!

from PyQt5 import QtCore, QtGui, QtWidgets

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(802, 692)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.label_2 = QtWidgets.QLabel(self.centralwidget)
        self.label_2.setGeometry(QtCore.QRect(310, 150, 211, 51))
        font = QtGui.QFont()
        font.setFamily("Agency FB")
        font.setPointSize(14)
        font.setBold(True)
        font.setWeight(75)
        self.label_2.setFont(font)
        self.label_2.setText("")
        self.label_2.setObjectName("label_2")
        self.label = QtWidgets.QLabel(self.centralwidget)
        self.label.setGeometry(QtCore.QRect(180, 250, 101, 51))
        font = QtGui.QFont()
        font.setPointSize(11)
        self.label.setFont(font)
        self.label.setObjectName("label")
        self.lineEdit_sn = QtWidgets.QLineEdit(self.centralwidget)
        self.lineEdit_sn.setGeometry(QtCore.QRect(290, 260, 301, 41))
        font = QtGui.QFont()
        font.setPointSize(12)
        self.lineEdit_sn.setFont(font)
        self.lineEdit_sn.setObjectName("lineEdit_sn")
        self.button_OK = QtWidgets.QPushButton(self.centralwidget)
        self.button_OK.setGeometry(QtCore.QRect(280, 370, 112, 34))
        self.button_OK.setObjectName("button_OK")
        self.button_cancel = QtWidgets.QPushButton(self.centralwidget)
        self.button_cancel.setGeometry(QtCore.QRect(470, 370, 112, 34))
        self.button_cancel.setObjectName("button_cancel")
        self.label_3 = QtWidgets.QLabel(self.centralwidget)
        self.label_3.setGeometry(QtCore.QRect(290, 50, 301, 51))
        font = QtGui.QFont()
        font.setPointSize(18)
        font.setBold(True)
        font.setWeight(75)
        self.label_3.setFont(font)
        self.label_3.setObjectName("label_3")
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 802, 30))
        self.menubar.setObjectName("menubar")
        MainWindow.setMenuBar(self.menubar)
        self.statusbar = QtWidgets.QStatusBar(MainWindow)
        self.statusbar.setObjectName("statusbar")
        MainWindow.setStatusBar(self.statusbar)

        self.retranslateUi(MainWindow)
        QtCore.QMetaObject.connectSlotsByName(MainWindow)

    def retranslateUi(self, MainWindow):
        _translate = QtCore.QCoreApplication.translate
        MainWindow.setWindowTitle(_translate("MainWindow", "MainWindow"))
        self.label.setText(_translate("MainWindow", "输入"))
        self.button_OK.setText(_translate("MainWindow", "OK"))
        self.button_cancel.setText(_translate("MainWindow", "Cancel"))
        self.label_3.setText(_translate("MainWindow", "扫描输入"))