Renderer.castShadows  

// make the object not cast shadows
renderer.castShadows = false;

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
void Awake() {
renderer.castShadows = false;
}
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

def Awake():
renderer.castShadows = false