Python Coding Exercise #50: Working with Numbers

The question

This exercise is worth four points, and it is built in steps. Each part adds one more result to the same program.

Pre-task

Please write a program which asks the user for integer numbers. The program should keep asking for numbers until the user types in zero.

Please type in integer numbers. Type in 0 to finish.
Number: 5
Number: 22
Number: 9
Number: -2
Number: 0

Part 1: Count

After reading in the numbers the program should print out how many numbers were typed in. The zero at the end should not be included in the count.

You will need a new variable here to keep track of the numbers typed in.

Numbers typed in 4

Part 2: Sum

The program should also print out the sum of all the numbers typed in. The zero at the end should not be included in the calculation.

Numbers typed in 4
The sum of the numbers is 34

Part 3: Mean

The program should also print out the mean of the numbers. The zero at the end should not be included in the calculation. You may assume the user will always type in at least one valid non-zero number.

Numbers typed in 4
The sum of the numbers is 34
The mean of the numbers is 8.5

Part 4: Positives and negatives

The program should also print out statistics on how many of the numbers were positive and how many were negative. The zero at the end should not be included in the calculation.

Numbers typed in 4
The sum of the numbers is 34
The mean of the numbers is 8.5
Positive numbers 3
Negative numbers 1

Before coding: what to track

The program has to read the numbers in a loop, and use them after the loop. Each result needs something to be remembered while the loop runs:

Result	What it needs	When it is calculated
Count	A counter that goes up by 1 for every number	In the loop
Sum	A total that grows by each number	In the loop
Mean	The sum divided by the count	After the loop
Positives	A counter that goes up for every number above zero	In the loop
Negatives	A counter that goes up for every number below zero	In the loop

The mean doesn’t need its own variable in the loop, because it can be worked out from two things that are already tracked: the sum and the count.

The most important detail is the zero. It ends the loop, but it is not one of the numbers, so it must not be counted or added. To make sure of that, the if number == 0: break check has to come before any counting.

My Solution

numbers = []
positive_int = 0
negative_int = 0
print("Please type in integer numbers. Type in 0 to finish.")
while True:
    number = int(input("Number: "))
    if number == 0:
        break
    numbers.append(number)
    if number > 0:
        positive_int += 1
    elif number < 0:
        negative_int += 1
print(f"Numbers typed in {len(numbers)}")
print(f"The sum of the numbers is {sum(numbers)}")
print(f"The mean of the numbers is {sum(numbers)/len(numbers)}")
print(f"Positive numbers {positive_int}")
print(f"Negative numbers {negative_int}")

How My Solution Works

1. An empty list for storing values

numbers = [] creates an empty list. A list is a variable that holds many values, one after another. Inside the loop, numbers.append(number) adds the new number to the end of the list. After the sample, numbers is [5, 22, 9, -2].

Learn more about list manipulation in my blog post on lists, tuples, sets and dictionaries.

2. Counters for positive and negative integers

positive_int and negative_int both start at 0. In each round, the number is checked: if number > 0 adds 1 to positive_int, and elif number < 0 adds 1 to negative_int.

3. The if statement

if number == 0: break comes before numbers.append(number). So when the user types 0, the loop ends immediately, and the zero never reaches the list or the counters. (For while True and break, see Exercise #43.)

4. The results come from the list after the loop

Everything that needs the whole set of numbers is worked out after the loop, using two built-in functions on the list:

• len(numbers) gives how many numbers there are, which is the count. (len() was introduced in Exercise #30.)
• sum(numbers) adds all the numbers together.

The mean is sum(numbers)/len(numbers), which is the sum divided by the count: 34 / 4 = 8.5. The positives and negatives are printed from their counters.

Following the sample

Round	The user types	numbers after	positive_int	negative_int
1	5	[5]	1	0
2	22	[5, 22]	2	0
3	9	[5, 22, 9]	3	0
4	-2	[5, 22, 9, -2]	3	1
5	0	unchanged	3	1

After the loop: the count is 4, the sum is 5 + 22 + 9 − 2 = 34, the mean is 34 / 4 = 8.5, and there are 3 positive and 1 negative numbers.

University Solution

print("Please type in integer numbers. Type in 0 to finish.")
numbers = 0
sum = 0
positives = 0

while True:
    number = int(input("Number: "))
    if number == 0:
        break
    numbers += 1
    sum += number
    if number>0:
        positives += 1

print("Numbers typed in", numbers)
print("The sum of the numbers is", sum)
print("The mean of the numbers is", sum/numbers)
print("Positive numbers", positives)
print("Negative numbers", numbers-positives)

The University Solution gets the same results without a list. Instead, it keeps three plain numbers that it updates in the loop:

• numbers is the count. It goes up by 1 for each number typed. In My Solution, the count is len(numbers).
• sum is a running total. It adds each new number to itself with sum += number, so after the sample it is 34. In My Solution, the total is sum(numbers).
• positives is a counter for numbers above zero, as in mine.
• The negatives are not counted at all. They are worked out at the end: numbers - positives. Since the zero was never counted, every number typed is either positive or negative, so the negatives are what is left after taking out the positives. For the sample, that is 4 − 3 = 1.

It also prints with commas inside print(), for example print("Numbers typed in", numbers), which puts a space between the text and the value, so the output is identical to the f-strings in My Solution. (See Exercise #05 for how commas and spaces work in print().)

List or counters?

	My Solution	University Solution
Keeps the numbers	Yes, in a list	No, only the count and the total
Count	len(numbers)	numbers += 1 in the loop
Sum	sum(numbers)	sum += number in the loop
Negatives	Own counter	numbers - positives

Both programs printed identical output for every set of numbers tested, including the sample, only positive numbers, only negative numbers, and numbers that add up to zero. The list version keeps all the numbers, so it is easier to do more with them later, such as finding the largest. The counters version only keeps what the exercise asks for.

Things to notice

The mean is always a float. The / operator gives a decimal result, even when it divides evenly. So three numbers adding up to 9 give 3.0, not 3.

The mean fails if the first number is zero. If the user types 0 straight away, the count is 0, and Python can’t divide by 0. Both programs stop with a ZeroDivisionError. The exercise says you may assume at least one non-zero number is typed, so it doesn’t need to be handled here.

The University Solution uses sum as a variable name. sum is also the name of Python’s built-in function that adds up a list, which My Solution uses. Once a variable is called sum, the name no longer means the function. Calling sum([1, 2]) afterwards gives TypeError: 'int' object is not callable. It works in this program because the function is never needed, but it’s safer to use another name, such as total. The same name is used again in Exercise #53.

elif number < 0 could be a plain else. The zero has already been dealt with by the break, so a number that isn’t above zero must be below it. I wrote elif number < 0 to make the meaning clear.

Key takeaways

• A loop can collect several results at once: a counter, a total, and more.
• Check for the stop value first, and break before any counting, so the stop value isn’t included.
• A list can hold all the numbers, and len() and sum() give the count and the total.
• A counter and a running total can replace a list when only the count and the total are needed.
• The mean is the sum divided by the count, and it is worked out after the loop.
• If every number is either positive or negative, the negatives are the count minus the positives.
• Don’t use the name of a built-in function, like sum, for your own variable.

✦ This is part of my Python Practice Exercise series, where I work through exercises while learning Python and explain each answer in plain language. ✦

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Practice Source: This exercise is taken from the Python Programming MOOC 2026 by the University of Helsinki. I’m working through the exercises as part of my Python learning journey and documenting my answers and explanations here.