Is movieclip moving?

1

im trying to make a function that tells me if my movieclip is moving

var thisPosition:Vector = new Vector(this.px,this.py);
			if(thisPosition.x == lastPosition.x && thisPosition.y == lastPosition.y){
				//movieclip isnt moving!
			}else{
				//inMotion = true;
			}
			lastPosition = new Vector(this.px,this.py);

but it doesnt work! how come? im using as3 btw