// The object whose rotation we want to match.
    var target: Transform;
    
    // Angular speed in degrees per sec.
    var speed: float;
    
    function Update () {    
        // The step size is equal to speed times frame time.
        var step = speed * Time.deltaTime;
        
        // Rotate our transform a step closer to the target's.
        transform.rotation = Quaternion.RotateTowards(transform.rotation, target.rotation, step);
    }

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public Transform target;
    public float speed;
    void Update() {
        float step = speed * Time.deltaTime;
        transform.rotation = Quaternion.RotateTowards(transform.rotation, target.rotation, step);
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public target as Transform

    public speed as single

    def Update():
        step as single = (speed * Time.deltaTime)
        transform.rotation = Quaternion.RotateTowards(transform.rotation, target.rotation, step)