python 2.7 - maximum recursion depth error? -

so i'm new (3 days) , i'm on code academy, i've written code 1 of activities when run it displays maximum recursion depth error, i'm running in python console of code academy , simultaneously on own ipython console. hint on page not helpful, can explain how fix this?

def hotel_cost(nights):     return (nights * 140)  def plane_ride_cost(city):     if plane_ride_cost("charlotte"):         return (183)     if plane_ride_cost("tampa"):         return (220)     if plane_ride_cost("pittsburgh"):         return (222)     if plane_ride_cost("loas angeles"):         return (475)  def rental_car_cost(days):     cost = days * 40     if days >= 7:         cost -= 50     elif days >= 3:         cost -= 20     return cost      def trip_cost(city, days):     return hotel_cost(nights) + plane_ride_cost(city) + rental_car_cost(days) 

maybe:

def plane_ride_cost(city):     if city == "charlotte":         return (183)     if city == "tampa":         return (220)     if city == "pittsburgh":         return (222)     if city == "los angeles":         return (475) 

the error was:

the plane_ride_cost(city) called plane_ride_cost("charlotte") in every recursion step.

not best, better approach:

def hotel_cost(nights):     return nights * 140  plane_cost = {     'charlotte' : 183,     'tampa' : 220,     'pittsburgh' : 222,     'los angeles' : 475, }  def plane_ride_cost(city):     if city not in plane_cost:         raise exception('city "%s" not registered.' % city)     else:         return plane_cost[city]  def rental_car_cost(days):     cost = days * 40     if days >= 7:         cost -= 50     elif days >= 3:         cost -= 20     return cost      def trip_cost(city, days):     return hotel_cost(nights) + plane_ride_cost(city) + rental_car_cost(days)