serial port - python send and receive data serially -

i'm trying communicate stm32l152rb board through com port 4 accepts commands com4 , displays result in terminal using code it's not working ... i'm new python please let me know i'm doing wrong.

#global variables ser = 0   def init_serial():     comnum = 4          #enter com port number here.     global ser          #must declared in each function     ser = serial.serial()     ser.baudrate = 9600     ser.port = comnum - 1   #com port name start 0      #ser.port = '/dev/ttyusb0' #if using linux      #specify timeout in seconds, serialport     #doesn't hangs     ser.timeout = 10     ser.open()          #opens serialport      # print port open or closed     if ser.isopen():         print 'dis' + ser.portstr     init_serial()  temp = raw_input('type want send, hit enter:\r\n') ser.write('dis')         #writes serialport  while 1:         bytes = ser.read()  #read serial port     print 'you sent: ' + bytes      #print read port