1.由designer设计实现的计算器类

文件名为：untitled.py

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

# Form implementation generated from reading ui file 'untitled.ui'
#
# Created by: PyQt5 UI code generator 5.15.9
#
# WARNING: Any manual changes made to this file will be lost when pyuic5 is
# run again.  Do not edit this file unless you know what you are doing.


from PyQt5 import QtCore, QtGui, QtWidgets


class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(241, 341)
        self.centralwidget = QtWidgets.QWidget(MainWindow)
        self.centralwidget.setObjectName("centralwidget")
        self.lcdNumber = QtWidgets.QLCDNumber(self.centralwidget)
        self.lcdNumber.setGeometry(QtCore.QRect(30, 40, 151, 31))
        font = QtGui.QFont()
        font.setBold(False)
        font.setUnderline(False)
        font.setWeight(50)
        font.setStrikeOut(False)
        self.lcdNumber.setFont(font)
        self.lcdNumber.setDigitCount(10)
        self.lcdNumber.setMode(QtWidgets.QLCDNumber.Dec)
        self.lcdNumber.setObjectName("lcdNumber")
        self.pushButton1 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton1.setGeometry(QtCore.QRect(30, 110, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButton1.setFont(font)
        self.pushButton1.setObjectName("pushButton1")
        self.pushButton2 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton2.setGeometry(QtCore.QRect(70, 110, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButton2.setFont(font)
        self.pushButton2.setObjectName("pushButton2")
        self.pushButton3 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton3.setGeometry(QtCore.QRect(110, 110, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButton3.setFont(font)
        self.pushButton3.setObjectName("pushButton3")
        self.pushButton4 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton4.setGeometry(QtCore.QRect(30, 140, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButton4.setFont(font)
        self.pushButton4.setObjectName("pushButton4")
        self.pushButton8 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton8.setGeometry(QtCore.QRect(70, 170, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButton8.setFont(font)
        self.pushButton8.setObjectName("pushButton8")
        self.pushButton5 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton5.setGeometry(QtCore.QRect(70, 140, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButton5.setFont(font)
        self.pushButton5.setObjectName("pushButton5")
        self.pushButton6 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton6.setGeometry(QtCore.QRect(110, 140, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButton6.setFont(font)
        self.pushButton6.setObjectName("pushButton6")
        self.pushButton7 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton7.setGeometry(QtCore.QRect(30, 170, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButton7.setFont(font)
        self.pushButton7.setObjectName("pushButton7")
        self.pushButton9 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton9.setGeometry(QtCore.QRect(110, 170, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButton9.setFont(font)
        self.pushButton9.setObjectName("pushButton9")
        self.pushButtonJiafa = QtWidgets.QPushButton(self.centralwidget)
        self.pushButtonJiafa.setGeometry(QtCore.QRect(150, 110, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButtonJiafa.setFont(font)
        self.pushButtonJiafa.setObjectName("pushButtonJiafa")
        self.pushButtonJianf = QtWidgets.QPushButton(self.centralwidget)
        self.pushButtonJianf.setGeometry(QtCore.QRect(150, 140, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButtonJianf.setFont(font)
        self.pushButtonJianf.setObjectName("pushButtonJianf")
        self.pushButtonChuaf = QtWidgets.QPushButton(self.centralwidget)
        self.pushButtonChuaf.setGeometry(QtCore.QRect(150, 200, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButtonChuaf.setFont(font)
        self.pushButtonChuaf.setObjectName("pushButtonChuaf")
        self.pushButtonX = QtWidgets.QPushButton(self.centralwidget)
        self.pushButtonX.setGeometry(QtCore.QRect(150, 170, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButtonX.setFont(font)
        self.pushButtonX.setObjectName("pushButtonX")
        self.pushButtonAnswer = QtWidgets.QPushButton(self.centralwidget)
        self.pushButtonAnswer.setGeometry(QtCore.QRect(110, 200, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButtonAnswer.setFont(font)
        self.pushButtonAnswer.setObjectName("pushButtonAnswer")
        self.pushButton0 = QtWidgets.QPushButton(self.centralwidget)
        self.pushButton0.setGeometry(QtCore.QRect(70, 200, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButton0.setFont(font)
        self.pushButton0.setObjectName("pushButton0")
        self.pushButtonClear = QtWidgets.QPushButton(self.centralwidget)
        self.pushButtonClear.setGeometry(QtCore.QRect(30, 200, 31, 21))
        font = QtGui.QFont()
        font.setBold(True)
        font.setUnderline(False)
        font.setWeight(75)
        self.pushButtonClear.setFont(font)
        self.pushButtonClear.setObjectName("pushButtonClear")
        self.line = QtWidgets.QFrame(self.centralwidget)
        self.line.setGeometry(QtCore.QRect(20, 240, 171, 16))
        self.line.setFrameShape(QtWidgets.QFrame.HLine)
        self.line.setFrameShadow(QtWidgets.QFrame.Sunken)
        self.line.setObjectName("line")
        self.line_2 = QtWidgets.QFrame(self.centralwidget)
        self.line_2.setGeometry(QtCore.QRect(20, 20, 171, 16))
        self.line_2.setFrameShape(QtWidgets.QFrame.HLine)
        self.line_2.setFrameShadow(QtWidgets.QFrame.Sunken)
        self.line_2.setObjectName("line_2")
        self.line_3 = QtWidgets.QFrame(self.centralwidget)
        self.line_3.setGeometry(QtCore.QRect(10, 30, 20, 221))
        self.line_3.setFrameShape(QtWidgets.QFrame.VLine)
        self.line_3.setFrameShadow(QtWidgets.QFrame.Sunken)
        self.line_3.setObjectName("line_3")
        self.line_4 = QtWidgets.QFrame(self.centralwidget)
        self.line_4.setGeometry(QtCore.QRect(180, 30, 20, 221))
        self.line_4.setFrameShape(QtWidgets.QFrame.VLine)
        self.line_4.setFrameShadow(QtWidgets.QFrame.Sunken)
        self.line_4.setObjectName("line_4")
        MainWindow.setCentralWidget(self.centralwidget)
        self.menubar = QtWidgets.QMenuBar(MainWindow)
        self.menubar.setGeometry(QtCore.QRect(0, 0, 241, 22))
        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.pushButton1.setText(_translate("MainWindow", "1"))
        self.pushButton2.setText(_translate("MainWindow", "2"))
        self.pushButton3.setText(_translate("MainWindow", "3"))
        self.pushButton4.setText(_translate("MainWindow", "4"))
        self.pushButton8.setText(_translate("MainWindow", "8"))
        self.pushButton5.setText(_translate("MainWindow", "5"))
        self.pushButton6.setText(_translate("MainWindow", "6"))
        self.pushButton7.setText(_translate("MainWindow", "7"))
        self.pushButton9.setText(_translate("MainWindow", "9"))
        self.pushButtonJiafa.setText(_translate("MainWindow", "+"))
        self.pushButtonJianf.setText(_translate("MainWindow", "-"))
        self.pushButtonChuaf.setText(_translate("MainWindow", "/"))
        self.pushButtonX.setText(_translate("MainWindow", "x"))
        self.pushButtonAnswer.setText(_translate("MainWindow", "="))
        self.pushButton0.setText(_translate("MainWindow", "0"))
        self.pushButtonClear.setText(_translate("MainWindow", "c"))

2.实现计算器类的实例化，窗口展示并添加逻辑功能

import sys
from untitled import Ui_MainWindow #引入在designer里编辑的类
from PyQt5.QtCore import *         #包含了包的核心的非gui功能
from PyQt5.QtGui import *

from PyQt5.QtWidgets import *      #包含了ui元素组件

#实体化designer里编辑的类，然后在继承
class calculator(QMainWindow, Ui_MainWindow):
    def __init__(self):
        super().__init__()
        self.num_cal = 0
        self.setupUi(self)
        self.num1 = 0
        self.num2 = 0

    #触发器的固定格式
    @pyqtSlot()
    def on_pushButton1_clicked(self):
        self.lcdNumber.display(int(self.lcdNumber.value()*10+1))
        # print(self.lcdNumber.value())
    @pyqtSlot()
    def on_pushButton2_clicked(self):
        self.lcdNumber.display(int(self.lcdNumber.value()*10+2))
    @pyqtSlot()
    def on_pushButton3_clicked(self):
        self.lcdNumber.display(int(self.lcdNumber.value()*10+3))
    @pyqtSlot()
    def on_pushButton4_clicked(self):
        self.lcdNumber.display(int(self.lcdNumber.value()*10+4))
    @pyqtSlot()
    def on_pushButton5_clicked(self):
        self.lcdNumber.display(int(self.lcdNumber.value()*10+5))
    @pyqtSlot()
    def on_pushButton6_clicked(self):
        self.lcdNumber.display(int(self.lcdNumber.value()*10+6))
    @pyqtSlot()
    def on_pushButton7_clicked(self):
        self.lcdNumber.display(int(self.lcdNumber.value()*10+7))
    @pyqtSlot()
    def on_pushButton8_clicked(self):
        self.lcdNumber.display(int(self.lcdNumber.value()*10+8))
    @pyqtSlot()
    def on_pushButton9_clicked(self):
        self.lcdNumber.display(int(self.lcdNumber.value()*10+9))
    @pyqtSlot()
    def on_pushButton0_clicked(self):
        self.lcdNumber.display(int(self.lcdNumber.value()*10+0))


    @pyqtSlot()
    def on_pushButtonJiafa_clicked(self):
        if(self.num_cal == 0):
            self.num1 = self.lcdNumber.value()
            # print(num1)
        # else:
        #     self.num2 = self.lcdNumber.value()
            # print(num2)
        self.num_cal = '+'
        print(self.num_cal)
        self.lcdNumber.display(0)


    @pyqtSlot()
    def on_pushButtonJianf_clicked(self):
        self.num1 = self.lcdNumber.value()
        self.num_cal = '-'

        self.lcdNumber.display(0)
    @pyqtSlot()
    def on_pushButtonX_clicked(self):
        self.num1 = self.lcdNumber.value()
        self.num_cal = '*'
        self.lcdNumber.display(0)
    @pyqtSlot()
    def on_pushButtonChuaf_clicked(self):
        self.num1 = self.lcdNumber.value()
        self.num_cal = '/'
        self.lcdNumber.display(0)

    @pyqtSlot()
    def on_pushButtonClear_clicked(self):
        self.lcdNumber.display(0)

    @pyqtSlot()
    def on_pushButtonAnswer_clicked(self):
        self.num2 = self.lcdNumber.value()
        if self.num_cal == '+':
            ans = self.num1 + self.num2
            print(ans)
            print(self.num2)
            self.lcdNumber.display(ans)
        elif self.num_cal == '-':
            ans = self.num1 - self.num2
            print(ans)
            print(self.num2)
            self.lcdNumber.display(ans)
        elif self.num_cal == '*':
            ans = self.num1 * self.num2
            print(ans)
            print(self.num2)
            self.lcdNumber.display(ans)
        elif self.num_cal == '/':
            ans = self.num1 / self.num2
            print(ans)
            print(self.num2)
            self.lcdNumber.display(ans)

if __name__ == '__main__':
    app = QApplication(sys.argv)
    ui = calculator()
    ui.show()
    sys.exit(app.exec_())

3.效果展示

4.总结：

QApplication:

QApplication 类管理图形用户界面应用程序的控制流和主要设置。 可以说 QApplication是Qt的整个后台管理的命脉

app = QApplication(sys.argv)这句作用用来初始化窗口系统 

app.exec():

app.exec_()的作用是运行主循环，必须调用此函数才能开始事件处理，调用该方法进入程序的主循环直到调用exit（）结束。主事件循环从窗口系统接收事件，并将其分派给应用程序小部件。如果没有该方法，那么在运行的时候还没有进入程序的主循环就直接结束了，所以运行的时候窗口会闪退。
app.exec_()在退出时会返回状态代码

sys.exit(n): 

不用sys.exit(app.exec_()),只使用app.exec_()，程序也可以正常运行，但是关闭窗口后进程却不会退出。

sys.exit(n)的作用是退出应用程序并返回n到父进程。

 参考文章：

原文链接：https://blog.csdn.net/cuicui_ruirui/article/details/102873528