使用自带的函数就可以实现：
lineEdit.setEchoMode(QLineEdit.Password)

import struct
from PyQt5.QtWidgets import (QMessageBox, QLineEdit)
from PyQt5.QtGui import QPixmap
{…}

class LoginWindow(QtWidgets.QWidget):
{…}
def init (self):
super(LoginWindow, self). init ()
# 加载ui文件
loadUi(‘login.ui’, self)
# 设置背景图片
background = QPixmap(“img/login_background.jpeg”)
background = background.scaled(self.background_label.width(),self.background_label.width())
self.background_label.setPixmap(background)
# 设置输入密码框
self.passwd_lineEdit.setEchoMode(QLineEdit.Password)
{…}

def mainpage():
app = QtWidgets.QApplication(sys.argv)
login_window = LoginWindow()
login_window.show()