Python: Loops (for and while) Worksheet

Question 1

What does this code print? for i in range(4):     print(i)

Accepted Answer

The code prints 0, 1, 2, and 3 on separate lines. In Python, range(4) starts at 0 and stops before 4.

Question 2

Write a for loop that prints the numbers 1 through 5, one number per line.

Accepted Answer

One correct answer is: for number in range(1, 6):     print(number) This works because range(1, 6) includes 1, 2, 3, 4, and 5.

Question 3

What does this code print? count = 3 while count > 0:     print(count)     count = count - 1 print("Go!")

Accepted Answer

The code prints 3, 2, 1, and then Go! on separate lines. The while loop runs while count is greater than 0.

Question 4

Choose the better loop type for this task and explain why: Print each item in a list of favorite foods.

Accepted Answer

A for loop is the better choice because the program needs to visit each item in a list. For loops are useful when looping through a sequence.

Question 5

Choose the better loop type for this task and explain why: Keep asking a user for a password until they type the correct password.

Accepted Answer

A while loop is the better choice because the number of guesses is not known ahead of time. The loop should continue while the password is incorrect.

Question 6

Fill in the blank so the loop prints 2, 4, 6, 8, and 10. for n in range(2, 11, ____):     print(n)

Accepted Answer

The blank should be 2. The code range(2, 11, 2) counts by 2 from 2 up to 10.

Question 7

Trace this code and write the final value of total. total = 0 for n in range(1, 4):     total = total + n

Accepted Answer

The final value of total is 6. The loop adds 1, then 2, then 3, so total becomes 0 + 1 + 2 + 3.

Question 8

This code is supposed to print 1, 2, and 3, but it has a bug. Fix it. x = 1 while x <= 3:     print(x)

Accepted Answer

The fixed code is: x = 1 while x <= 3:     print(x)     x = x + 1 The original code caused an infinite loop because x never changed.

Question 9

What does this code print? for letter in "cat":     print(letter)

Accepted Answer

The code prints c, a, and t on separate lines. A for loop can loop through each character in a string.

Question 10

Write a while loop that prints the numbers 5 down to 1, one number per line.

Accepted Answer

One correct answer is: number = 5 while number >= 1:     print(number)     number = number - 1 This works because the variable starts at 5 and decreases by 1 each time.

Question 11

Look at this code. for i in range(3):     print("Hello") How many times does it print Hello?

Accepted Answer

It prints Hello 3 times. The loop runs once for each value in range(3), which is 0, 1, and 2.

Question 12

Complete the code to print each animal in the list. animals = ["dog", "cat", "rabbit"] for animal in animals:     __________

Accepted Answer

The blank should be print(animal). The completed loop prints each animal in the list on its own line.

Question 13

What is the value of x after this code runs? x = 10 while x < 20:     x = x + 3

Accepted Answer

The final value of x is 22. The values are 10, 13, 16, 19, and then 22, and the loop stops because 22 is not less than 20.

Question 14

Write a for loop that prints the square of each number from 1 through 4. The output should be 1, 4, 9, and 16 on separate lines.

Accepted Answer

One correct answer is: for n in range(1, 5):     print(n * n) This prints the square of each number from 1 through 4.

Question 15

Explain the difference between a for loop and a while loop in Python. Give one example of when each loop type is useful.

Accepted Answer

A for loop is useful when you know the sequence you want to loop through, such as numbers in a range or items in a list. A while loop is useful when you want to repeat until a condition changes, such as asking for input until the user gives a correct answer.

Python: Loops (for and while)

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