I am looking into design patterns and best practices, especially on class composition (see my old question). I have a specific example where I found it really hard to implement a good OOP design for.
Say there the concept of a garage which holds cars and there is a call to an external service whose response gives information about each car present in a garage.
This is an example response I want to capture and create classes for:
[{'carID': '1x148i-36y5-5rt2',
'carDimensions': {'top': 275,
'left': 279,
'width': 75,
'height': 75},
'carAttributes': {'weight': {'weightLevel': 'medium',
'value': 1.6},
'topSpeed': {'sppedLevel': 'good',
'value': 0.7},
'noise': {'noiseLevel': 'low',
'value': 0.32},
'accessories': [{'optionsLevel': 'poor',
'quality': 2.8}]}},
{'carID': '223a3-33e5-4ea3',
'carDimensions': {'top': 241,
'left': 234,
'width': 71,
'height': 65},
'carAttributes': {'weight': {'weightLevel': 'light',
'value': 1.1},
'topSpeed': {'sppedLevel': 'great',
'value': 1.6},
'noise': {'noiseLevel': 'high',
'value': 0.97},
'accessories': [{'optionsLevel': 'great',
'quality': 3.2}]}}]
Below are my class design approach.
I tried creating a Car class that extracts each field like so:
class `Car`:
def __init__(self, car_response_dictionary):
self.car = car_response_dictionary
def get_carID(self):
return self.car.get("carID")
# etc.
and another class to handle some calculations based on the carDimensions:
class Size:
def __init__(self, top, left, width, height):
self.top = top
self.left = left
self.width = width
self.height = height
def get_coordinates(self):
bottom = self.left + self.height
right = self.top + self.width
return (self.left, self.top), (bottom, right)
and a class to capture the concept of a garage which holds a list of Car objects:
class Garage:
def __init__(self, datestamp, cars):
self.datestamp = datestamp
self.cars = cars
# do stuff based on cars
So, my idea is to create an instance of a Garage and get the response list in cars, I try to unpack each car as a Car instance object by iterating through the cars list of dictionaries and -using class composition- create a Car instance for each car.
At this point I find impossible to implement my design in Python and I think that maybe the approach in my design is to be blamed or my poor understanding of class composition.
If someone could provide a simple code implementation for the above example that would be very educational for me. Even if that means that new design is proposed (e.g. I was contemplating of making a Response class).
Below are few classes and a 'main' that uses a composition (using the Size class as a data member of Car class).
#
# Note that the code does not use 'dict' as an argument for the Car __init__
# but it can be easily modified and use dict as input
#
class Car:
def __init__(self, id, weight, top_speed, noise, size):
self.id = id
self.weight = weight
self.top_speed = top_speed
self.noise = noise
self.size = size
def get_id(self):
return self.id
def __str__(self):
return 'id: {} weight: {} top speed: {} noise: {} size: {}'.format(self.id, self.weight, self.top_speed,
self.noise,
self.size)
class Size:
def __init__(self, top, left, width, height):
self.top = top
self.left = left
self.width = width
self.height = height
def get_coordinates(self):
bottom = self.left + self.height
right = self.top + self.width
return (self.left, self.top), (bottom, right)
def __str__(self):
return '[top: {} left: {} width: {} height: {}]'.format(self.top, self.left, self.width, self.height)
class Garage:
def __init__(self):
self.cars_holder = {}
def add_car(self, car):
self.cars_holder[car.get_id()] = car
def remove_car(self, car_id):
del self.cars_holder[car_id]
def show_cars(self):
for car in self.cars_holder.values():
print(car)
GARAGE_AS_DICT = [{'id': '1x148i-36y5-5rt2',
'dimensions': {'top': 275,
'left': 279,
'width': 75,
'height': 75},
'attrs': {'weight': 12,
'top_speed': 0.7,
'noise': 0.45
}},
{'id': '223a3-33e5-4ea3',
'dimensions': {'top': 241,
'left': 234,
'width': 71,
'height': 65},
'attrs': {'weight': 12,
'top_speed': 0.74,
'noise': 0.4345
}
}]
if __name__ == "__main__":
garage = Garage()
for dict_car in GARAGE_AS_DICT:
attrs = dict_car['attrs']
dimensions = dict_car['dimensions']
garage.add_car(Car(dict_car['id'], attrs['weight'], attrs['top_speed'], attrs['noise'],
Size(dimensions['top'], dimensions['left'], dimensions['width'], dimensions['height'])))
garage.show_cars()
Output:
id: 223a3-33e5-4ea3 weight: 12 top speed: 0.74 noise: 0.4345 size: [top: 241 left: 234 width: 71 height: 65]
id: 1x148i-36y5-5rt2 weight: 12 top speed: 0.7 noise: 0.45 size: [top: 275 left: 279 width: 75 height: 75]