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