Vusa Moyo wrote:
> I have a suspicion my lecturer's question is flawed, so I'd like to pose
> it to you guys to confirm my suspicions.
>
> Here goes..
>
> I've gone and created a Class Cat1(cat): <-- inherited class, but cant
> seem get the code right which allows the test code to run successfully.
Is the following...
> We have a class defined for cats. Create a new cat called cat1. Set cat1
> to be a grey Burmese cat worth 3000 with the name Whiskers.
your task? Then your lecturer may be asking you to *instantiate* the Cat
class, not to make a subclass.
> # define the Cat class
>
> class Cat:
> name = ""
>
> kind = "cat"
> color = ""
> value = 100.00
The above are all class attributes. This is unusual, as even two cates of
the same race will have a different name and value. If I'm guessing right
your solution will look more like
$ cat cars.py
class Car:
def __init__(self, make, color, year):
self.make = make
self.color = color
self.year = year
def __str__(self):
return "{0.color} {0.make}".format(self)
def __repr__(self):
return (
"Car(color={0.color}, "
"make={0.make}, "
"year={0.year})"
).format(self)
carpark = [
Car("Ford", "blue", 1973),
Car("Volkswagen", "yellow", 2003)
]
print(carpark) # uses Car.__repr__
print()
print("In our car park we have")
for car in carpark:
print(" - a", car) # uses Car.__str__
$ python3 cars.py
[Car(color=blue, make=Ford, year=1973), Car(color=yellow, make=Volkswagen,
year=2003)]
In our car park we have
- a blue Ford
- a yellow Volkswagen
$
>From the view of the script a VW and a Ford work the same, so there is no
need to introduce subclasses, but if you're asked to do it anyway here's one
way:
$ cat cars2.py
class Car:
def __init__(self, color, year):
self.color = color
self.year = year
def __str__(self):
return "{0.color} {0.make}".format(self)
def __repr__(self):
return (
"{classname}(color={0.color}, "
"year={0.year})"
).format(self, classname=self.__class__.__name__)
class Ford(Car):
make = "Ford"
class Volkswagen(Car):
make = "VW"
carpark = [
Ford("blue", 1973),
Volkswagen("yellow", 2003)
]
print(carpark) # uses Car.__repr__
print()
print("In our car park we have")
for car in carpark:
print(" - a", car) # uses Car.__str__
$ python3 cars2.py
[Ford(color=blue, year=1973), Volkswagen(color=yellow, year=2003)]
In our car park we have
- a blue Ford
- a yellow VW
$
However, this is the kind of inheritance you will only ever see in textbook
examples because the subclasses do not introduce differing features. As a
rule of thumb there should be at least one method with a fundamentally
different implementation, or one extra method that is not shared between
baseclass and subclass.
> def description(self):
> desc_str = "%s is a %s %s cat worth R%.2f." % (self.name, self.color,
> self.kind, self.value)
>
> return desc_str
>
> # your code goes here
>
>
> # test code
>
> print(cat1.description())
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