在QWidget python GUI上绘制一个圆

import sys
from PyQt5.QtWidgets import QApplication, QWidget
from PyQt5.QtGui import QPainter, QColor, QPen
from PyQt5.QtCore import Qt

class MyWidget(QWidget):
    def __init__(self):
        super().__init__()
        self.setWindowTitle('绘制圆')
        self.setGeometry(100, 100, 400, 400)
        
    def paintEvent(self, event):
        painter = QPainter(self)
        painter.setRenderHint(QPainter.Antialiasing)  # 抗锯齿
        
        # 设置画笔
        pen = QPen()
        pen.setWidth(2)
        pen.setColor(QColor(0, 0, 255))  # 蓝色
        pen.setStyle(Qt.SolidLine)  # 实线
        painter.setPen(pen)
        
        # 设置画刷
        brush = QBrush()
        brush.setColor(QColor(255, 0, 0))  # 红色
        brush.setStyle(Qt.SolidPattern)  # 实心
        painter.setBrush(brush)
        
        # 绘制圆
        center = self.rect().center()  # 窗口中心点
        radius = min(self.width(), self.height()) // 2  # 半径为窗口宽高的最小值的一半
        painter.drawEllipse(center, radius, radius)
        
if __name__ == '__main__':
    app = QApplication(sys.argv)
    widget = MyWidget()
    widget.show()
    sys.exit(app.exec_())