Attribute Error: object has no attribute in python

Question

I have the following class Ui_MainWindow(object). However I get the Attribute Error, that AttributeError: 'Ui_MainWindow' object has no attribute 'ser' .ser is before defindet in the check_phone() method. The problem occurs in the sendMessage() method. How comes that .ser is not recognized anymore?

    from PyQt5 import QtCore, QtGui, QtWidgets

    import Tkinter as tk
    import tkFileDialog as filedialog
    import tkMessageBox
    import serial
    import time

class Ui_MainWindow(object):
    def setupUi(self, MainWindow):
        MainWindow.setObjectName("MainWindow")
        MainWindow.resize(503, 486)
        self.pushButton_2 = QtWidgets.QPushButton(self.widget)
        self.pushButton_2.setObjectName("pushButton_2")
        self.gridLayout.addWidget(self.pushButton_2, 3, 2, 1, 1)
        self.pushButton_2.clicked.connect(self.send_sms) #send sms function

    def check_phone(self):
         ser = serial.Serial('/dev/ttyACM0', 
                 460800, 
                 timeout=5, 
                 xonxoff = False,   
                 rtscts = False, 
                 bytesize = serial.EIGHTBITS, 
                 parity = serial.PARITY_NONE, 
                 stopbits = serial.STOPBITS_ONE)

    def sendMessage(self):
        self.ser.write('ATZ\r')
        time.sleep(1)
        self.ser.write('AT+CMGF=1\r')
        time.sleep(1)
        self.ser.write('''AT+CMGS="''' + self.recipient + '''"\r''')
        time.sleep(1)
        self.ser.write(self.content + "\r")
        time.sleep(1)
        self.ser.write(chr(26))
        time.sleep(2)

    def send_sms(self):
    check = self.radioButton.isChecked() #stuff doesnt work yet!
    test =  self.lineEdit.text()
    print(test)
    if check == True:
        if not self.lineEdit.text():
            root = tk.Tk()
            root.withdraw()
            tkMessageBox.showwarning("Phone Number Missing!", "Please enter a valid phone number")
            root.destroy()
            root.mainloop()
            return
        if not self.plainTextEdit.toPlainText():
            root = tk.Tk()
            root.withdraw()
            tkMessageBox.showwarning("Message Missing!", "Please enter a text message")
            root.destroy()
            root.mainloop()
            return
        else:
            sms = Ui_MainWindow(self.lineEdit.text(), self.plainTextEdit.toPlainText())
            sms.check_phone()
            sms.sendMessage()
            sms.disconnectPhone()
            self.plainTextEdit2.setText('message sent successfully')

Answer 1

As Jon points out, you're assigning serial.Serial to a (soon-discarded) local variable in check_phone rather than to an instance attribute.

Replace this:

def check_phone(self):
     ser = serial.Serial('/dev/ttyACM0', 
             460800, 
             timeout=5, 
             xonxoff = False,   
             rtscts = False, 
             bytesize = serial.EIGHTBITS, 
             parity = serial.PARITY_NONE, 
             stopbits = serial.STOPBITS_ONE)

With this:

def check_phone(self):
     self.ser = serial.Serial('/dev/ttyACM0', 
             460800, 
             timeout=5, 
             xonxoff = False,   
             rtscts = False, 
             bytesize = serial.EIGHTBITS, 
             parity = serial.PARITY_NONE, 
             stopbits = serial.STOPBITS_ONE)