import sys
from PyQt5.QtWidgets import QWidget, QApplication

app = QApplication(sys.argv)
widget = QWidget()
widget.resize(640, 480)
widget.setWindowTitle("Hello, PyQt5!")
widget.show()
sys.exit(app.exec())

from PyQt5.QtWidgets import QApplication,QMainWindow
from mainwindow import Ui_MainWindow
import sys

class My_UI(QMainWindow, Ui_MainWindow):
 def __init__(self):
 QMainWindow.__init__(self)
 Ui_MainWindow.__init__(self)
 self.setupUi(self)

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

 # 显示窗口
 win = My_UI()
 win.show()
 sys.exit(app.exec_())

class CommonHelper:
 def __init__(self):
 pass

 @staticmethod
 def readQss(style):
 with open(style, 'r') as f:
 return f.read()

if __name__ == '__main__':
 app = QApplication(sys.argv)
 # 设置style
 styleFile = './css.qss'
 qssStyle = CommonHelper.readQss(styleFile)
 app.setStyleSheet(qssStyle)
 # 显示窗口
 win = My_UI()
 win.show()
 sys.exit(app.exec_())

QPushButton {
 box-shadow: inset 0px 1px 0px 0px #ffffff;
 background: linear-gradient(to bottom, #f9f9f9 5%, #e9e9e9 100%);
 background-color: #f9f9f9;
 border-radius: 6px;
 border: 1px solid #dcdcdc;
 display: inline-block;
 cursor: pointer;
 color: #666666;
 font-family: Arial;
 font-size: 15px;
 font-weight: bold;
 padding: 4px 15px;
 text-decoration: none;
 text-shadow: 0px 1px 0px #ffffff;
}

QPushButton:hover {
 background: linear-gradient(to bottom, #e9e9e9 5%, #f9f9f9 100%);
 background-color: #e9e9e9;
}

QPushButton:pressed {
 position: relative;
 top: 1px;
}