Python Pyserial problem ?

Hi ,
I have a problem with connecting arduino serial with USB.

Windows 7 X64 [ I tried on other x32 windows 7 computer too ] Python 2.7 Pyserial installed.

Arduino UI and Processing UI i could access to serial and read HelloWorld from Serial monitor.

http://www.ftdichip.com/Drivers/VCP.htm X64 certified driver installed.

On pyhton console no error messages returned. [ if i live com port open from Arduino UI it returns port is using , i think serial connection works ]

Arduino Code

int ledPin = 13; // select the pin for the LED
int i=0; // simple counter to show we're doing something

void setup() {
pinMode(ledPin,OUTPUT); // declare the LED's pin as output
Serial.begin(9600); // connect to the serial port
}

void loop () {
Serial.print(i++);
Serial.println(" Hello world!"); // print out a hello
digitalWrite(ledPin, HIGH);
delay(500);
digitalWrite(ledPin, LOW);
delay(500);
}

Python Kodu
import serial
ser = serial.Serial('com3', 9600)
while 1:
ser.readline()

Any ideas about problem ?

O solved problem. It's related about rebooting arduino.
I add
ser.setRTS(False)
line and everything looks ok.