多个按钮在 PyQt5 python 中不起作用

您需要为窗口指定布局并将小部件添加到其中：

import sys
from PyQt5.QtWidgets import QMainWindow, QApplication, QWidget, QPushButton, QAction, QLineEdit, QMessageBox, \
    QVBoxLayout
from PyQt5.QtGui import QIcon
from PyQt5.QtCore import pyqtSlot


class MainWindow(QMainWindow):
    def __init__(self):
        super().__init__()
        self.initUI()

    def initUI(self):
        self.setWindowTitle('Calculator')
        self.setGeometry(100, 100, 4000, 1400)

        self.layout = QVBoxLayout(self)
        self.setLayout(self.layout)

        self.num1 = QLineEdit(self)
        self.num1.move(20, 20)
        self.num1.resize(280, 40)
        self.layout.addChildWidget(self.num1)

        self.num2 = QLineEdit(self)
        self.num2.move(20, 100)
        self.num2.resize(280, 40)
        self.layout.addChildWidget(self.num2)

        # minus button
        self.minus = QPushButton('-', self)
        self.minus.move(80, 180)
        self.minus.resize(20, 40)
        self.minus.clicked.connect(self.minus_onclick)
        self.layout.addChildWidget(self.minus)

        # plus button
        self.plus = QPushButton('+', self)
        self.plus.move(20, 180)
        self.plus.resize(20, 40)
        self.plus.clicked.connect(self.plus_onclick)
        self.layout.addChildWidget(self.plus)

        # * button
        self.into = QPushButton('*', self)
        self.into.move(140, 180)
        self.into.resize(20, 40)
        self.into.clicked.connect(self.into_onclick)
        self.layout.addChildWidget(self.into)

        # division button
        self.div = QPushButton('/', self)
        self.div.move(140, 180)
        self.div.resize(20, 40)
        self.div.clicked.connect(self.div_onclick)
        self.layout.addChildWidget(self.div)

    def plus_onclick(self):
        if isinstance(self.num1.text(), int):
            num1 = int(self.num1.text())
            op = '+'

    def minus_onclick(self):
        if isinstance(self.num1.text(), int):
            num1 = int(self.num1.text())
            op = '-'

    def into_onclick(self):
        if isinstance(self.num1.text(), int):
            num1 = int(self.num1.text())
            op = '*'

    def div_onclick(self):
        if isinstance(self.num1.text(), int):
            num1 = int(self.num1.text())
            op = '/'


if __name__ == '__main__':
    app = QApplication(sys.argv)
    mainWindow = MainWindow()
    mainWindow.show()

    sys.exit(app.exec_())

此外，最好show在类构造函数之外调用。

希望能帮助到你。