I'm doing exercises on pynative.com. The url is: https://pynative.com/python-object-oriented-programming-oop-exercise/#h-oop-exercise-4-class-inheritance
I'm stuck on OOP Exercise 4: Class Inheritance.
Here are the given instructions: Given:
Create a Bus class that inherits from the Vehicle class. Give the capacity argument of Bus.seating_capacity() a default value of 50.
Use the following code for your parent Vehicle class.
Here's the given code:
class Vehicle:
def __init__(self, name, max_speed, mileage):
self.name = name
self.max_speed = max_speed
self.mileage = mileage
def seating_capacity(self, capacity):
return f"The seating capacity of a {self.name} is {capacity} passengers"
Here is the expected output:
The seating capacity of a bus is 50 passengers
Here's the solution that was provided on the website:
class Vehicle:
def __init__(self, name, max_speed, mileage):
self.name = name
self.max_speed = max_speed
self.mileage = mileage
def seating_capacity(self, capacity):
return f"The seating capacity of a {self.name} is {capacity} passengers"
class Bus(Vehicle):
# assign default value to capacity
def seating_capacity(self, capacity=50):
return super().seating_capacity(capacity=50)
School_bus = Bus("School Volvo", 180, 12)
print(School_bus.seating_capacity())
What I dont get is why the default for capacity was declared twice. Also I'm not getting why super() was declared.
I tried to remove the default declaration from capacity from both lines (I played around with it a bit), but I kept getting errors.
def seating_capacity(self, capacity=50): return super().seating_capacity(capacity=50)
Yeah, this is nonsense. The first capacity=50 declares a parameter with the default value 50. The second capacity=50 passes the value 50 to the named parameter capacity for the call to super().seating_capacity. Either of those by itself is fine, but both together make no sense here, since the first parameter-with-default-value isn't being used for anything. Correctly it should be:
def seating_capacity(self, capacity=50):
return super().seating_capacity(capacity)
This is overriding the parent's seating_capacity method, providing a default value for the capacity parameter, then calls the parent's seating_capacity implementation, passing it the capacity value (which may be the default 50 or whatever the caller passed to School_bus.seating_capacity(..)).
Even this is debatable from a SOLID perspective, as it changes the function signature of seating_capacity from requiring an argument to not requiring one; but at least that doesn't break anything per se.