14 KiB
Classes in Python¶
First, let's consider some data in a plain Python dictionary:
car1 = {
'name': 'Fer',
'worth': 60000,
'type_': 'convertible',
'color': 'red'
}
car2 = {
'name': 'Jump',
'worth': 10000,
'type_': 'van',
'color': 'blue'
}
car1['name']
Now, let's make a Python class which will hold this same kind of data:
class Car:
def __init__(self,name,worth,type_,color):
self.name = name
self.worth = worth
self.type_ = type_
self.color = color
def print_car(self):
print("%s is worth %d and is a %s %s."%(self.name, self.worth, self.color, self.type_))
car1 = Car("Fer",60000,"convertible","red")
Takeaway message¶
- The data in an instances of a class are conceptually very similar to python dicts with a few special features. One of these special features is methods. Another is that you access instance variables with with the
x_instance.namesyntax instead ofx_dict['name']syntax.
Q1 creating an instance of a class¶
We have a class defined for vehicles. Create two new vehicles ("instances of the class") with the variable names car1 and car2. Set car1 to be a red convertible worth EUR 60,000.00 with a name of Fer, and car2 to be a blue van named Jump worth EUR 10,000.00.
class Vehicle:
def __init__(self, color, worth, name):
self.color = color
self.worth = worth
self.name = name
def get_description(self):
return 'name: {}, worth: {}, color: {}'.format(self.name, self.worth, self.color)
# YOUR CODE HERE
raise NotImplementedError()
# This checks if your code works. Do not change it. It should run without error.
assert( car1.get_description()=="name: Fer, worth: 60000, color: red" )
assert( car2.get_description()=="name: Jump, worth: 10000, color: blue" )
Q2 creating a class¶
Create a class called Pet. The __init__ function should take 3 arguments: self, name, and sound. The name, and sound arguments should be assigned to the instance variables self.name and self.sound.
# YOUR CODE HERE
raise NotImplementedError()
# This checks if your code works. Do not change it. It should run without error.
my_pet = Pet('Bob', 'talk')
assert(my_pet.name=='Bob')
assert(my_pet.sound=='talk')
Q3 writing a method¶
Now, create a new class called NoisyPet. The __init__ function should be like in Pet. (It takes 3 arguments: self, name, and sound. The name, and sound arguments should be assigned to the instance variables self.name and self.sound.)
NoisyPet should have an additional method called make_noise which takes zero additional arguments (of course self is required). The make_noise for a name of "cricket" and sound of "chirp", this method should return a string like "My pet cricket makes a noise like chirp". Thus, you will need to return a string you have created using string formatting.
# YOUR CODE HERE
raise NotImplementedError()
# This checks if your code works. Do not change it. It should run without error.
assert(NoisyPet("cricket", "chirp").make_noise()=="My pet cricket makes a noise like chirp")
Q4 using instances 1¶
Now create a list named my_pets with 5 instances of the NoisyPet class given the following names and noises.
| name | noise |
|---|---|
| Fido | slobber |
| Mr. Skinny Legs | (silent) |
| cricket | chirp |
| Adelheid | cackle |
| Bello | bark |
# YOUR CODE HERE
raise NotImplementedError()
# This checks if your code works. Do not change it. It should run without error.
assert(type(my_pets)==list)
assert(len(my_pets)==5)
for my_pet in my_pets:
assert(isinstance(my_pet,NoisyPet))
my_pet.make_noise()
Q5 using instances 2¶
Now create a function list named get_pet_name_length which takes a single argument, which is an instance of the NoisyPet class. It should return the number of letters in the pet's name.
# YOUR CODE HERE
raise NotImplementedError()
# This checks if your code works. Do not change it. It should run without error.
assert(get_pet_name_length(NoisyPet("Bello", "bark"))==5)
assert(get_pet_name_length(NoisyPet("cricket", "chirp"))==7)