Sending float from arduino to raspberry pi using Wire (arduino) and smbus (python) libraries

Send multiple floats from Arduino to Raspberry through I2C

http://bradsrpi.blogspot.fr/2013/03/sending-data-from-arduino-to-raspberry.html

i2c_float.c

#include <Wire.h>

#define SLAVE_ADDRESS 0x04

#define FLOATS_SENT 2

float temperature = 10.5;
float luminosity = 5.2;
float data[FLOATS_SENT];

void setup() {
    pinMode(13, OUTPUT);
    Serial.begin(9600);
    
    data[0] = temperature;
    data[1] = luminosity;
    
    // initialize i2c as slave
    Wire.begin(SLAVE_ADDRESS);

    // define callbacks for i2c communication
    Wire.onRequest(sendData);
}

void loop() {
    delay(100);
}

void sendData(){
  Wire.write((byte*) &temperature, FLOATS_SENT*sizeof(float));
}

i2c_float.py

import time
import struct

import smbus

# for RPI version 1, use "bus = smbus.SMBus(0)"
bus = smbus.SMBus(1)

# This is the address we setup in the Arduino Program
address = 0x04


def get_data():
    return bus.read_i2c_block_data(address, 0, 8)


def get_float(data, index):
    bytes = data[4*index:(index+1)*4]
    return struct.unpack('f', "".join(map(chr, bytes)))[0]


while True:
    try:
        data = get_data()
        print(get_float(data, 0))
        print(get_float(data, 1))
    except Exception as e:
        print(e)
        continue
    finally:
        time.sleep(1)

I am also late to the party ;-) hopefully there is still somebody around.

Basically, it does exactly what I want. The modification
read_i2c_block_data(address, 0, 8);
is essential (and python would not complain about the semicolon???).
Otherwise, without the third parameter, the Arduino runs wild and keeps sending 255 and would not stop.

But I have a problem:
The parameter "cmd", which is 0 in this case, is not understood by the Arduino.
When reading from the raspi, the Arduino confuses this 0 with other incoming data.
So this solution works one-way only.

I found another solution here:
https://stackoverflow.com/questions/14420372/how-to-read-data-from-arduino-with-raspberry-pi-with-i2c?rq=2

i2c_msg can be used to request the amount of data needed.

Wow, thanks for the interest in the script !

I cleaned up the script and implemented the read size based on @wicusverhoef's suggestion. However I can't test it right now, I count on you lads :)