Practice Quiz: Object-oriented Programming (Optional)
1. Let’s test your knowledge of using dot notation to access methods and attributes in an object. Let’s say we have a class called Birds. Birds has two attributes: color and number. Birds also has a method called count() that counts the number of birds (adds a value to number). Which of the following lines of code will correctly print the number of birds? Keep in mind, the number of birds is 0 until they are counted!
- bluejay.number = 0
print(bluejay.number)
- print(bluejay.number.count())
- bluejay.count()
print(bluejay.number)
- print(bluejay.number)
2. Creating new instances of class objects can be a great way to keep track of values using attributes associated with the object. The values of these attributes can be easily changed at the object level. The following code illustrates a famous quote by George Bernard Shaw, using objects to represent people. Fill in the blanks to make the code satisfy the behavior described in the quote.
# “If you have an apple and I have an apple and we exchange these apples then
# you and I will still each have one apple. But if you have an idea and I have
# an idea and we exchange these ideas, then each of us will have two ideas.”
# George Bernard Shaw
class Person:
apples = 0
ideas = 0
johanna = Person()
johanna.apples = 1
johanna.ideas = 1
martin = Person()
martin.apples = 2
martin.ideas = 1
def exchange_apples(you, me):
#Here, despite G.B. Shaw’s quote, our characters have started with #different amounts of apples so we can better observe the results.
#We’re going to have Martin and Johanna exchange ALL their apples with #one another.
#Hint: how would you switch values of variables,
#so that “you” and “me” will exchange ALL their apples with one another?
#Do you need a temporary variable to store one of the values?
#You may need more than one line of code to do that, which is OK.
___
return you.apples, me.apples
def exchange_ideas(you, me):
#”you” and “me” will share our ideas with one another.
#What operations need to be performed, so that each object receives
#the shared number of ideas?
#Hint: how would you assign the total number of ideas to
#each idea attribute? Do you need a temporary variable to store
#the sum of ideas, or can you find another way?
#Use as many lines of code as you need here.
you.ideas ___
me.ideas ___
return you.ideas, me.ideas
exchange_apples(johanna, martin)
print(“Johanna has {} apples and Martin has {} apples”.format(johanna.apples, martin.apples))
exchange_ideas(johanna, martin)
print(“Johanna has {} ideas and Martin has {} ideas”.format(johanna.ideas, martin.ideas))
- class Person:
apples = 0
ideas = 0
johanna = Person()
johanna.apples = 1
johanna.ideas = 1
martin = Person()
martin.apples = 1 # Martin also starts with 1 apple, as per the quote
martin.ideas = 1
def exchange_apples(you, me):
# Exchange all apples
temp = you.apples
you.apples = me.apples
me.apples = temp
return you.apples, me.apples
def exchange_ideas(you, me):
# Share ideas
you.ideas += me.ideas
me.ideas = you.ideas
return you.ideas, me.ideas
exchange_apples(johanna, martin)
print(“Johanna has {} apples and Martin has {} apples”.format(johanna.apples, martin.apples))
exchange_ideas(johanna, martin)
print(“Johanna has {} ideas and Martin has {} ideas”.format(johanna.ideas, martin.ideas))
3. The City class has the following attributes: name, country (where the city is located), elevation (measured in meters), and population (approximate, according to recent statistics). Fill in the blanks of the max_elevation_city function to return the name of the city and its country (separated by a comma), when comparing the 3 defined instances for a specified minimal population. For example, calling the function for a minimum population of 1 million: max_elevation_city(1000000) should return “Sofia, Bulgaria”.
# define a basic city class
class City:
name = “”
country = “”
elevation = 0
population = 0
# create a new instance of the City class and
# define each attribute
city1 = City()
city1.name = “Cusco”
city1.country = “Peru”
city1.elevation = 3399
city1.population = 358052
# create a new instance of the City class and
# define each attribute
city2 = City()
city2.name = “Sofia”
city2.country = “Bulgaria”
city2.elevation = 2290
city2.population = 1241675
# create a new instance of the City class and
# define each attribute
city3 = City()
city3.name = “Seoul”
city3.country = “South Korea”
city3.elevation = 38
city3.population = 9733509
def max_elevation_city(min_population):
# Initialize the variable that will hold
# the information of the city with
# the highest elevation
return_city = City()
# Evaluate the 1st instance to meet the requirements:
# does city #1 have at least min_population and
# is its elevation the highest evaluated so far?
if ___
return_city = ___
# Evaluate the 2nd instance to meet the requirements:
# does city #2 have at least min_population and
# is its elevation the highest evaluated so far?
if ___
return_city = ___
# Evaluate the 3rd instance to meet the requirements:
# does city #3 have at least min_population and
# is its elevation the highest evaluated so far?
if ___
return_city = ___
#Format the return string
if return_city.name:
return ___
else:
return “”
print(max_elevation_city(100000)) # Should print “Cusco, Peru”
print(max_elevation_city(1000000)) # Should print “Sofia, Bulgaria”
print(max_elevation_city(10000000)) # Should print “”
- # define a basic city class
class City:
name = “”
country = “”
elevation = 0
population = 0
# create a new instance of the City class and
# define each attribute
city1 = City()
city1.name = “Cusco”
city1.country = “Peru”
city1.elevation = 3399
city1.population = 358052
# create a new instance of the City class and
# define each attribute
city2 = City()
city2.name = “Sofia”
city2.country = “Bulgaria”
city2.elevation = 2290
city2.population = 1241675
# create a new instance of the City class and
# define each attribute
city3 = City()
city3.name = “Seoul”
city3.country = “South Korea”
city3.elevation = 38
city3.population = 9733509
def max_elevation_city(min_population):
# Initialize the variable that will hold
# the information of the city with
# the highest elevation
return_city = None
# Iterate over each city and compare its population
# with the minimum population, and if it satisfies the
# requirement, check whether its elevation is greater
# than the previously found city. If it is, update the
# highest elevation city.
for city in [city1, city2, city3]:
if city.population >= min_population and (not return_city or city.elevation > return_city.elevation):
return_city = city
# Format the return string
if return_city:
return”{}, {}”.format(return_city.name, return_city.country)
else:
return””
print(max_elevation_city(100000)) # Should print “Cusco, Peru”
print(max_elevation_city(1000000)) # Should print “Sofia, Bulgaria”
print(max_elevation_city(10000000)) # Should print “”
4. What makes an object different from a class?
- An object represents and defines a concept
- An object is a specific instance of a class
- An object is a template for a class
- Objects don’t have accessible variables
5. We have two pieces of furniture: a brown wood table and a red leather couch. Fill in the blanks following the creation of each Furniture class instance, so that the describe_furniture function can format a sentence that describes these pieces as follows: “This piece of furniture is made of {color} {material}”
class Furniture:
color = “”
material = “”
table = Furniture()
___
___
couch = Furniture()
___
___
def describe_furniture(piece):
return (“This piece of furniture is made of {} {}”.format(piece.color, piece.material))
print(describe_furniture(table))
# Should be “This piece of furniture is made of brown wood”
print(describe_furniture(couch))
# Should be “This piece of furniture is made of red leather”
- class Furniture:
color = “”
material = “”
table = Furniture()
table.color = “brown”
table.material = “wood”
couch = Furniture()
couch.color = “red”
couch.material = “leather”
def describe_furniture(piece):
return (“This piece of furniture is made of {} {}”.format(piece.color, piece.material))
print(describe_furniture(table))
# Should be “This piece of furniture is made of brown wood”
print(describe_furniture(couch))
# Should be “This piece of furniture is made of red leather”
