Function to filter flights by airline, route, or date

def filter_flights(flight_data, airline=None, route=None, date=None):
filtered_flights = flight_data
if airline:
filtered_flights = [flight for flight in filtered_flights if flight["airline"] == airline]
if route:
filtered_flights = [flight for flight in filtered_flights if flight["route"] == route]
if date:
filtered_flights = [flight for flight in filtered_flights if flight["date"] == date]
return filtered_flights