plot - Python ser.readline() not reading incoming data from arduino via usb -

first time posting here apologize if posted incorrectly.

so i'm trying make digital stethoscope , plot data live via python. have stethoscope mic shoved inside hooked breadboard mic test circuit. goes arduino sends data via usb laptop. python code can display incoming data live awesome. problem when tap on stethoscope, incoming data should change. if i'm displaying serial data via arduino or minicom, data change when hit stethoscope. when @ python plot data doesn't change , can't figure out why. here code;

arduino

int sensorvalue = 0;  //value read pot  void setup() {   //init serial communications @ 115200 bps;   serial.begin(9600);  }  void loop() {   //read a0   sensorvalue = analogread(a0);    //serial.write(sensorvalue);    //serial.print("the voltage is: ");   serial.println(sensorvalue);   //serial.println("v"); } 

python

import serial import numpy np import matplotlib.pyplot plt drawnow import *  voltarray = [] count = 0 arduinodata = serial.serial('/dev/ttyacm0',9600) plt.ion()   def makefig():     plt.title('stethascope data')     plt.plot(voltarray,'bo-')     plt.grid(true)     plt.ylabel('voltage (v)')     plt.ylim(0,5)   while true:      while (arduinodata.inwaiting()==0): #wait here until there data         pass #do nothing      arduinostring = arduinodata.readline()     print arduinostring       try:         volt = float(arduinostring)      except valueerror: #        pass         print 'valueerror'      print 'pin value: ', volt      volt = volt*(5.0/1024.0) #arduino reads 0-5v, 10bit resolution                              #2^10 = 1024, arduino outputs 0-1023      print 'voltage: ', volt      voltarray.append(volt) #append volt value array      drawnow(makefig)      count = count + 1      if (count > 50):         voltarray.pop(0)       print 'end loop'     print 

anybody have ideas?