Functions & Abstraction
What is abstraction in programming, and how do functions support it?
Abstraction hides complex logic and lets you focus on key tasks. Functions support abstraction by packaging reusable code behind a name.
What is the difference between a function that prints a value and one that returns it?
Printing displays the result; returning gives the value back for reuse.
Explain in your own words what a recursive function does and when you might use one.
It calls itself to solve smaller versions of a problem, e.g., factorial.
How many elements (indices) are in this list? What is its last element?
myList = ['dog', 'cat', 'fish', 'lizard']
4 elements; last is 'lizard'
How is a tuple different from a list? What happens if you try to modify it?
Tuples are immutable. You get an error if you try to change them.
Count how many times the letter 'a' appears:
word = 'banana'
Use word.count('a') #result is 3
Here's a function header. Fill in the body so it prints 'Welcome, <name>!':
def welcome(name):
def welcome(name):
print(f"Welcome, {name}!")
Complete the function to return the average of two numbers:
def average(a, b):
def average(a, b):
return (a + b) / 2
What's the base case of this function?
def countdown(n):
if n == 0:
print('Blast off!')
else:
countdown(n-1)
The base case is when n == 0.
What will this code output?
myList = [10, 20, 30]
myList[1] = 50
print(myList)
[10, 50, 30]
Create a dictionary to store these student scores: Alice: 91, Bob: 87, Chris: 78
{'Alice': 91, 'Bob': 87, 'Chris': 78}
What does this return? Why?
msg = 'hello world'
print(msg.find('z'))
-1 because 'z' isn't in the string.
How does this function demonstrate code reuse?
def say_hello():
print('Hello!')
say_hello()
say_hello()
The same code runs twice with one definition, showing reuse.
Explain what happens here:
def square(x):
return x * x
def add_one(n):
return n + 1
result = add_one(square(3))
print(result)
square(3) returns 9;
add_one(9) returns 10;
result is 10.
Describe what's happening step-by-step:
def mystery(n):
if n == 1:
return 1
else:
return n + mystery(n-1)
print(mystery(4))
Adds 4 + 3 + 2 + 1 = 10
What will the slice return?
myList = [0, 1, 2, 3, 4, 5]
print(myList[2:5])
[2, 3, 4]
What does this return and why?
d = {'x': 1, 'y': 2}
print(list(d.items()))
[('x', 1), ('y', 2)] it shows key-value pairs as tuples.
What does this print?
msg = 'python'
print(msg[1:4])
'yth' #index 1 to before 4
This function is called inside another. What is the output?
def shout():
print('HEY!')
def greet():
print('Hello')
shout()
greet()
Hello
HEY!
Write a function called 'safe_divide' that returns the result of a / b. If b is 0, return 'undefined'.
def safe_divide(a,b):
if b == 0:
return 'undefined'
else:
return a / b
Why does this recursive function crash?
def broken(n):
return n + broken(n - 1)
No base case to stop recursion. It runs forever.
Update each value in this list so that it becomes double its original value:
nums = [1, 2, 3, 4]
Use a loop:
for i in range(len(nums)):
nums[i] *= 2
How can you avoid a KeyError when accessing a value in this dictionary?
my_dictionary = {'fruit': 'apple'}
print(my_dictionary['vegetable'])
Use
if "vegetable" in my_dictionary:
Why does this cause an error?
name = 'Sam'
name[0] = 'B'
Strings are immutable; you can't assign to a character.
Why does the following code give an error?
def greet():
message = 'Hi'
greet()
print(message)
'message' is local to greet() and doesn't exist outside it.
Why is this function not working as expected?
def calc_area(length, width):
area = length * width
result = calc_area(5, 2)
print(result)
It doesn't return anything, so result is None. Use 'return area'.
Complete this recursive factorial function:
def factorial(n):
def factorial(n):
if n == 0:
return 1
else:
return n * factorial(n - 1)
What mistake might a student make here?
myList = []
for i in range(3):
myList.append(i)
print(myList)
No mistake here; it prints [0, 1, 2], but they might forget to initialize myList.
You have the following tuple:
t = (150, 250)
How could you convert this tuple into a dictionary?
d = dict([t])
How do you check if two strings are exactly equal in Python?
Use the == operator:
string1 == string2