PaintEvent触发了几次我的代码

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__()

    def paintEvent(self, event):
        painter = QPainter(self)
        painter.setPen(QPen(Qt.black, 2, Qt.SolidLine))
        painter.setBrush(QColor(255, 255, 255))
        painter.drawRect(10, 10, 100, 100)

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