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I write a program to that send and recive data from serial, but I have a problem, I want to create a function "connect()" or a class, and when I press a button, the function is executed, but if I create this function in "MainWindow" class, variable "ser" from "TestThread" class become uninitialized, can you help me?

import sys
import serial


from PyQt5.QtWidgets import QMainWindow, QApplication
from PyQt5.QtCore import QThread, pyqtSignal
from PyQt5.uic import loadUi


ser = serial.Serial('/dev/tty.usbmodem14201', 9600, timeout=1)

class TestThread(QThread):
 serialUpdate = pyqtSignal(str)
 def run(self):
 while ser.is_open:
 QThread.sleep(1)
 value = ser.readline().decode('ascii')
 self.serialUpdate.emit(value)
 ser.flush()

class MainWindow(QMainWindow):
 def __init__(self):
 super(MainWindow, self).__init__()
 loadUi('/Users/bogdanvesa/P2A_GUI/mainwindow.ui', self)
 self.thread = TestThread(self)
 self.thread.serialUpdate.connect(self.handleSerialUpdate)

 self.connect_btn.clicked.connect(self.connectSer)
 self.lcd_EBtn.clicked.connect(self.startThread)

 def startThread(self):
 self.thread.start()

 def handleSerialUpdate(self, value):
 print(value)
 self.lcd_lineEdit.setText(value)


def main():

 app = QApplication(sys.argv)
 form = MainWindow()
 form.show()
 sys.exit(app.exec_())

if __name__ == "__main__":
 main()

Instead of using pySerial + thread it is better to use QSerialPort that is made to live with the Qt event-loop:

from PyQt5 import QtCore, QtWidgets, QtSerialPort

class Widget(QtWidgets.QWidget):
 def __init__(self, parent=None):
 super(Widget, self).__init__(parent)
 self.message_le = QtWidgets.QLineEdit()
 self.send_btn = QtWidgets.QPushButton(
 text="Send",
 clicked=self.send
 )
 self.output_te = QtWidgets.QTextEdit(readOnly=True)
 self.button = QtWidgets.QPushButton(
 text="Connect", 
 checkable=True,
 toggled=self.on_toggled
 )
 lay = QtWidgets.QVBoxLayout(self)
 hlay = QtWidgets.QHBoxLayout()
 hlay.addWidget(self.message_le)
 hlay.addWidget(self.send_btn)
 lay.addLayout(hlay)
 lay.addWidget(self.output_te)
 lay.addWidget(self.button)

 self.serial = QtSerialPort.QSerialPort(
 '/dev/tty.usbmodem14201',
 baudRate=QtSerialPort.QSerialPort.Baud9600,
 readyRead=self.receive
 )

 @QtCore.pyqtSlot()
 def receive(self):
 while self.serial.canReadLine():
 text = self.serial.readLine().data().decode()
 text = text.rstrip('rn')
 self.output_te.append(text)

 @QtCore.pyqtSlot()
 def send(self):
 self.serial.write(self.message_le.text().encode())

 @QtCore.pyqtSlot(bool)
 def on_toggled(self, checked):
 self.button.setText("Disconnect" if checked else "Connect")
 if checked:
 if not self.serial.isOpen():
 if not self.serial.open(QtCore.QIODevice.ReadWrite):
 self.button.setChecked(False)
 else:
 self.serial.close()

if __name__ == '__main__':
 import sys
 app = QtWidgets.QApplication(sys.argv)
 w = Widget()
 w.show()
 sys.exit(app.exec_())