思路：每次输入框内容改变，都重置 QTimer 倒计时为 3 秒；当持续 3 秒无输入后，QTimer 超时，获取当前输入框内容。
UI 代码（untitled.py）：
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from PyQt5 import QtCore, QtGui, QtWidgetsclass Ui_Form(object):def setupUi(self, Form):Form.setObjectName("Form")Form.resize(400, 300)self.horizontalLayout = QtWidgets.QHBoxLayout(Form)self.horizontalLayout.setObjectName("horizontalLayout")self.verticalLayout = QtWidgets.QVBoxLayout()self.verticalLayout.setObjectName("verticalLayout")self.plain_text_edit = QtWidgets.QPlainTextEdit(Form)self.plain_text_edit.setObjectName("plainTextEdit")self.verticalLayout.addWidget(self.plain_text_edit)self.label = QtWidgets.QLabel(Form)self.label.setText("")self.label.setAlignment(QtCore.Qt.AlignLeading|QtCore.Qt.AlignLeft|QtCore.Qt.AlignVCenter)self.label.setObjectName("label")self.verticalLayout.addWidget(self.label)self.verticalLayout.setStretch(0, 1)self.verticalLayout.setStretch(1, 1)self.horizontalLayout.addLayout(self.verticalLayout)self.retranslateUi(Form)QtCore.QMetaObject.connectSlotsByName(Form)def retranslateUi(self, Form):_translate = QtCore.QCoreApplication.translateForm.setWindowTitle(_translate("Form", "Form"))
逻辑代码：
import sysfrom PyQt5.QtWidgets import *
from PyQt5.QtCore import *from untitled import Ui_Form # UI 代码：untitled.pyclass MyWindow(QWidget, Ui_Form):def __init__(self):super(MyWindow, self).__init__()self.setupUi(self)self.plain_text_edit.textChanged.connect(self.set_timer) # 检测输入框文本改变self.timer = QTimer()self.timer.setSingleShot(True) # 设置为单次触发，即定时器超时后只触发一次，避免多余触发self.timer.timeout.connect(self.get_text) # 超时（3000ms）后获取当前输入框内容def set_timer(self):print("重置 timer 倒计时为 3000ms")self.timer.start(3000)def get_text(self):print("读取 plain_text_edit 文本，并设置到 label 中")self.label.setText(self.plain_text_edit.toPlainText())app = QApplication(sys.argv)
mw = MyWindow()
mw.show()
sys.exit(app.exec_())