PyQt5计时器点击重置按钮无法归零问题求助

你的计时器重置功能失效的核心问题在于时间计算依赖的起始时间从未被正确重置：

• 你定义了全局变量start = datetime.datetime.now()，这个值是程序启动时的固定时间，后续点击Start、Reset按钮都没有更新它。
• 点击Reset时，你只重置了显示的self.count和暂停标记self.flag，但当再次点击Start时，showTime方法依旧用程序启动时的start时间来计算流逝时间，导致计时器从之前累计的时长继续走。
• 另外，Start按钮只设置了self.flag = True，没有在每次启动时记录新的起始时间，这会导致暂停后再启动，时间会跳过暂停的时长，直接从程序启动的总流逝时间计算，这也是一个潜在问题。

把起始时间改成类的实例变量，在Start时记录当前时间，Reset时重置所有计时相关变量：

# importing libraries
from PyQt5.QtWidgets import * 
from PyQt5 import QtCore, QtGui
from PyQt5.QtGui import * 
from PyQt5.QtCore import * 
import sys
import datetime

class Window(QMainWindow):
  
    def __init__(self):
        super().__init__()
        self.setWindowFlags(QtCore.Qt.FramelessWindowHint)
        self.setAttribute(QtCore.Qt.WA_TranslucentBackground)
  
        # setting title
        self.setWindowTitle("Python Stop watch")
  
        # setting geometry
        self.setGeometry(100, 100, 400, 500)
  
        # calling method
        self.UiComponents()
  
        # showing all the widgets
        self.show()
  
    # method for widgets
    def UiComponents(self):
  
        # counter
        self.count = '{:02d}:{:02d}:{:02d}'.format(0,0,0)
        # 初始化实例变量的起始时间
        self.start_time = datetime.datetime.now()
        # 记录暂停时已经流逝的秒数
        self.elapsed_paused = 0
  
        # creating flag
        self.flag = False
  
        # creating a label to show the time
        self.label = QLabel(self)
  
        # setting geometry of label
        self.label.setGeometry(75, 100, 250, 70)
  
        # adding border to the label
        self.label.setStyleSheet("border : 4px solid black;")
  
        # setting text to the label
        self.label.setText(str(self.count))
  
        # setting font to the label
        self.label.setFont(QFont('Arial', 25))
  
        # setting alignment to the text of label
        self.label.setAlignment(Qt.AlignCenter)
  
        # creating start button
        start = QPushButton("Start", self)
  
        # setting geometry to the button
        start.setGeometry(125, 250, 150, 40)
  
        # add action to the method
        start.pressed.connect(self.Start)
  
        # creating pause button
        pause = QPushButton("Pause", self)
  
        # setting geometry to the button
        pause.setGeometry(125, 300, 150, 40)
  
        # add action to the method
        pause.pressed.connect(self.Pause)
  
        # creating reset button
        re_set = QPushButton("Re-set", self)
  
        # setting geometry to the button
        re_set.setGeometry(125, 350, 150, 40)
  
        # add action to the method
        re_set.pressed.connect(self.Re_set)
  
        # creating a timer object
        timer = QTimer(self)
  
        # adding action to timer
        timer.timeout.connect(self.showTime)
  
        # update the timer every tenth second
        timer.start(100)
  
    # method called by timer
    def showTime(self):
  
        # checking if flag is true
        if self.flag:
            # 计算当前流逝的总时间：暂停前的时长 + 本次启动后的时长
            current_elapsed = (datetime.datetime.now() - self.start_time).total_seconds() + self.elapsed_paused
            self.hour = int(current_elapsed // 3600)
            self.min = int(current_elapsed % 3600 // 60)
            self.seconds = int(current_elapsed % 60)
            self.count ='{:02d}:{:02d}:{:02d}'.format(self.hour, self.min, self.seconds)
            
  
        # getting text from count
        text = str(self.count)
  
        # showing text
        self.label.setText(text)
        
  
    def Start(self):
        # 启动时记录当前时间作为新的起始点
        self.start_time = datetime.datetime.now()
        # making flag to true
        self.flag = True
        
  
    def Pause(self):
        # 暂停时记录已经流逝的总时长
        if self.flag:
            self.elapsed_paused += (datetime.datetime.now() - self.start_time).total_seconds()
        # making flag to False
        self.flag = False
  
    def Re_set(self):
        # making flag to false
        self.flag = False
        # 重置暂停累计时长
        self.elapsed_paused = 0
        # reseeting the count
        self.count = '{:02d}:{:02d}:{:02d}'.format(0,0,0)
        # 重置起始时间为当前时间（避免后续启动时计算错误）
        self.start_time = datetime.datetime.now()
        # setting text to label
        self.label.setText(str(self.count))
    
  
# create pyqt5 app
App = QApplication(sys.argv)
  
# create the instance of our Window
window = Window()
  
# start the app
sys.exit(App.exec())

• 移除全局start变量，改用类实例变量self.start_time和self.elapsed_paused来管理计时状态
• Start按钮点击时，重新记录当前时间作为新的计时起始点
• Pause按钮点击时，累计已经流逝的时长，确保暂停后再启动能继续计时
• Reset按钮点击时，重置所有计时相关变量：暂停累计时长、起始时间、显示计数和标记

内容的提问来源于stack exchange，提问作者Abhishek Shahi