TextMesh.font  

// Set the text of the attached Text mesh
var newFont : Font;
GetComponent(TextMesh).font = newFont;

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public Font newFont;
    void Example() {
        GetComponent<TextMesh>().font = newFont;
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public newFont as Font

    def Example():
        GetComponent[of TextMesh]().font = newFont