Cubietruck, I2C Python

Hy,
I use Cubietruck / Armbian
I have a problem with I2C connecting to an Arduino.
my Python program returns me an error when I use the SMBus module :

read_byte_data the function (address, reg) bug while writing functions work well.

here is my Arduino code :

#include <Wire.h>
#include <LiquidCrystal.h>
#include <string.h>
#include <ctype.h>

const int RS = 12;
const int E = 11;
const int D4 = 5;
const int D5 = 4;
const int D6 = 3;
const int D7 = 2;
LiquidCrystal lcd(RS,E,D4,D5,D6,D7);



#define SLAVE_ADDRESS 0x12


byte regs[3];
int regIndex=0;
byte lastExecReq = 0x00;
char message[20];

void setup (void){
  regs[0] = 0x00;
  regs[1] = 0x00;
  regs[2] = 0x00;
  Wire.begin(SLAVE_ADDRESS);
  Wire.onReceive(receiveEvent);
  Wire.onRequest(requestEvent);
  Serial.begin(9600);
  lcd.begin(20,4);
  lcd.print ("LCD OK");
  sprintf(message,"Bus I2C 0x%02x Ready",SLAVE_ADDRESS);
  Serial.println(message);
  lcd.setCursor(0,1);
  lcd.print(message);
}

void loop(void){
  if (regs[0]==0x00){
    delay(100);
    return;
  }
  switch(regs[0]){
    case 0x01 : break;
    case 0x02 : break;
    case 0x03 : 
      if (regs[1]>0){
        lcd.setCursor(0,2);
        lcd.print("Start ...   ");
      }else{
        lcd.setCursor(0,2);
        lcd.print("Stop ...   ");
      }
      break;
  }
}
void receiveEvent(int byteCount){
  int byteCounter = 0;
  while (byteCounter<byteCount){
    byte b = Wire.read();
    byteCounter +=1;
    if (byteCounter == 1){
      regIndex = b;
    }
    else{
      switch(regIndex){
        case 0 :
          regs[0] = b;
          lastExecReq = b;
          break;
        case 1:
          regs[1]=b;
          break;
        case 2:
          regs[2]=b;
          break;
      }
    }
  }
}

void requestEvent(){
  switch(regIndex){
    case 0x00:
      switch (lastExecReq){
        case 0x01:
          Wire.write(0x03);
          break;
        case 0x02:
          Wire.write(regs[1]+regs[2]);
          break;
        default : Wire.write(0xFF);
      }
      break;
    default: Wire.write(0xFF);
  }
}

and here Python

#!/usr/bin/python
import re
import smbus
import time

address = 0x12

class Bus_I2C(object):
  def __init__(self,address,busnum=1,debug=False):
    self.address = address
    self.bus = smbus.SMBus(busnum)
    self.debug = debug
  def errMsg(self):
    print("access error 0x%02X: check your I2C address")%self.address
    return -1
  def write8(self,reg,value):
    try:
      self.bus.write_byte_data(self.address,reg,value)
      if self.debug :
        print("I2C : write 0x%02X in the reg 0x%02X")%(value,reg)
    except IOError,err:
        return self.errMsg()
  def writeList(self,reg,list):
    try:
      if self.debug:
        print("I2C : write a list in the reg 0x%02X:")%reg
        print(list)
      self.bus.write_i2c_block_data(self.address,reg,list)
    except IOError,err:
      return self.errMsg()
  def readU8(self,reg):
    try:
      result=self.bus.read_byte_data(self.address,reg)
      #result=self.bus.read_byte(self.address,reg)
      if self.debug:
        print("I2C : device 0x%02X returned 0x%02X from reg 0x%02X")%(self.address,result,reg)
      return result
    except IOError,err:
      return self.errMsg()

i2c = Bus_I2C(address,1,True)

print("///////////// 0x01 in reg 0")
i2c.write8(0,0x01)
time.sleep(0.200)
print("///////////// read reg ...")
print(i2c.readU8(0x00))
time.sleep(0.100)
print("///////////// start LCD ...")
i2c.write8(0x01,1)
time.sleep(0.02)
i2c.write8(0x00,0x03)
time.sleep(0.100)
time.sleep(5)
print("///////////// stop LCD ...")
i2c.write8(0x01,0)
time.sleep(0.02)
i2c.write8(0x00,0x03)
time.sleep(0.100)

where is the bug ?

thank for your help

geka