Arduino and Raspberry I2C Communication. Send String

i2c.ino

#include <Wire.h>
#define SLAVE_ADDRESS 0x2A

void setup() {
    // initialize i2c as slave
    Wire.begin(SLAVE_ADDRESS);
    Wire.onRequest(sendData); 
}

void loop() {
}

char data[] = "123456789123456";
int index = 0;

// callback for sending data
void sendData() { 
    Wire.write(data[index]);
    ++index;
    if (index >= 15) {
         index = 0;
    }
 }

i2c.py

#!/usr/bin/python

import smbus
import time
bus = smbus.SMBus(1)
address = 0x2a

while True:
    data = ""
    for i in range(0, 15):
            data += chr(bus.read_byte(address));
    print(data)
    time.sleep(1);