def make_flight_url(date_str, flight_num, route_num):
    """
    Takes date string, flight number, and route number, returns 
    URL to search for a particular flight/route/day. 
    ---
    IN: date string YYYYMMDD (str), 
        flight_num (str), 
        route_num (str)
    OUT: search URL (str)
    """

    # base URL constructors
    base_url1 = 'http://flightaware.com/live/flight/'
    base_url2 = '/history/'
    base_url3 = '/KLGA/KORD'
    
    # merge vars with URL bases
    search_url = (base_url1 + flight_num + base_url2 + 
                  date_str + '/' + route_num + base_url3)

    return search_url