Week 3 – Loops

Practice Quiz: While Loops

1. In Python, what do while loops do?

  • while loops tell the computer to repeatedly execute a set of instructions while a condition is true.
  • while loops instruct the computer to execute a piece of code a set number of times.
  • while loops branch execution based on whether or not a condition is true.
  • while loops initialize variables in Python.

2. Which techniques can prevent an infinite while loop? Select all that apply.

  • Change the value of a variable used in the while condition
  • Use the stop keyword
  • Use the break keyword
  • Use the continue keyword

3. The following code contains an infinite loop, meaning the Python interpreter does not know when to exit the loop once the task is complete. To solve the problem, you will need to:

Find the error in the code

Fix the while loop so there is an exit condition

Hint: Try running your function with the number 0 as the input and observe the result.

Note that Coursera’s code blocks will time out after 5 seconds of running an infinite loop. If you get this timeout error message, it means the infinite loop has not been fixed.

def is_power_of_two(number):
# This while loop checks if the "number" can be divided by two
# without leaving a remainder. How can you change the while loop to
# avoid a Python ZeroDivisionError?
while number % 2 == 0:
number = number / 2
# If after dividing by 2 "number" equals 1, then "number" is a power
# of 2.
if number == 1:
return True
return False

# Calls to the function
print(is_power_of_two(0)) # Should be False
print(is_power_of_two(1)) # Should be True
print(is_power_of_two(8)) # Should be True
print(is_power_of_two(9)) # Should be False

  • def is_power_of_two(number):
    if number == 0:
    returnFalse# Exit condition for zero input

    while number % 2 == 0:
    number = number / 2

    if number == 1:
    returnTrue

    returnFalse
     

    # Calls to the function
    print(is_power_of_two(0)) # Should be False
    print(is_power_of_two(1)) # Should be True
    print(is_power_of_two(8)) # Should be True
    print(is_power_of_two(9)) # Should be False

4. Fill in the blanks to complete the while loop so that it returns the sum of all the divisors of a number, without including the number itself. As a reminder, a divisor is a number that divides into another without a remainder. To do this, you will need to:

1. Initialize the "divisor" and "total" variables with starting values

2. Complete the while loop condition

3. Increment the "divisor" variable inside the while loop

4. Complete the return statement

# Fill in the blanks so that the while loop continues to run while the
# "divisor" variable is less than the "number" parameter.

def sum_divisors(number):
# Initialize the appropriate variables
___ = ___
___ = ___

# Avoid dividing by 0 and negative numbers
# in the while loop by exiting the function
# if "number" is less than one
if number < 1:
return 0

# Complete the while loop
while ___:
if number % divisor == 0:
total += divisor
# Increment the correct variable
___ += 1

# Return the correct variable
return ___


print(sum_divisors(0)) # Should print 0
print(sum_divisors(3)) # Should print 1
# 1
print(sum_divisors(36)) # Should print 1+2+3+4+6+9+12+18
# 55
print(sum_divisors(102)) # Should print 1+2+3+6+17+34+51
# 114

  • # Fill in the blanks so that the while loop continues to run while the
    # “divisor” variable is less than the “number” parameter.

    def sum_divisors(number):
    # Initialize the appropriate variables
    divisor = 1
    total = 0

    # Avoid dividing by 0 and negative numbers
    # in the while loop by exiting the function
    # if “number” is less than one
    if number < 1:
    return0

    # Complete the while loop
    while divisor < number:
    if number % divisor == 0:
    total += divisor
    # Increment the correct variable
    divisor += 1

    # Return the correct variable
    return total


    print(sum_divisors(0)) # Should print 0
    print(sum_divisors(3)) # Should print 1
    # 1
    print(sum_divisors(36)) # Should print 1+2+3+4+6+9+12+18
    # 55
    print(sum_divisors(102)) # Should print 1+2+3+6+17+34+51
    # 114

5. Fill in the blanks to complete the function, which should output a multiplication table. The function accepts a variable “number” through its parameters. This “number” variable should be multiplied by the numbers 1 through 5, and printed in a format similar to “1x6=6” (“number” x “multiplier” = “result”). The code should also limit the “result” to not exceed 25. To satisfy these conditions, you will need to:

1. Initialize the “multiplier" variable with the starting value

2. Complete the while loop condition

3. Add an exit point for the loop

4. Increment the “multiplier" variable inside the while loop
def multiplication_table(number):
# Initialize the appropriate variable
___ = ___

# Complete the while loop condition.
while ___:
result = number * multiplier
if result > 25 :
# Enter the action to take if the result is greater than 25
___
print(str(number) + "x" + str(multiplier) + "=" + str(result))
# Increment the appropriate variable
___ += 1


multiplication_table(3)
# Should print:
# 3x1=3
# 3x2=6
# 3x3=9
# 3x4=12
# 3x5=15

multiplication_table(5)
# Should print:
# 5x1=5
# 5x2=10
# 5x3=15
# 5x4=20
# 5x5=25

multiplication_table(8)
# Should print:
# 8x1=8
# 8x2=16
# 8x3=24

  • def multiplication_table(number):
    # Initialize the appropriate variable
    multiplier = 1

    # Complete the while loop condition.
    while multiplier <= 5:
    result = number * multiplier
    if result > 25 :
    # Enter the action to take if the result is greater than 25
    break
    print(str(number) + “x” + str(multiplier) + “=” + str(result))
     
    # Increment the appropriate variable
    multiplier += 1


    multiplication_table(3)
    # Should print:
    # 3×1=3
    # 3×2=6
    # 3×3=9
    # 3×4=12
    # 3×5=15

    multiplication_table(5)
    # Should print:
    # 5×1=5
    # 5×2=10
    # 5×3=15
    # 5×4=20
    # 5×5=25

    multiplication_table(8)
    # Should print:
    # 8×1=8
    # 8×2=16
    # 8×3=24
Next

Devendra Kumar

Project Management Apprentice at Google

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