OnTriggerStay is called once per frame for every Collider other that is touching the trigger.

This message is sent to the trigger and the collider that touches the trigger. Note that trigger events are only sent if one of the colliders also has a rigid body attached.

	// Applies an upwards force to all rigidbodies that enter the trigger.
	function OnTriggerStay (other : Collider) {
		if (other.attachedRigidbody)
			other.attachedRigidbody.AddForce(Vector3.up * 10);
	}

using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void OnTriggerStay(Collider other) {
        if (other.attachedRigidbody)
            other.attachedRigidbody.AddForce(Vector3.up * 10);
        
    }
}

import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def OnTriggerStay(other as Collider) as void:
		if other.attachedRigidbody:
			other.attachedRigidbody.AddForce((Vector3.up * 10))

OnTriggerStay can be a co-routine, simply use the yield statement in the function.