Lesson 3 of 10

Module 3 · Python for Beginners

Numbers and Maths

Do arithmetic in Python: the operators, whole-number division and remainders, the order of operations, rounding, useful built-in functions, the math module and formatting money.

About 35 minutes

Open in ColabEvery example as a notebook you can run, edit and save to your Google Drive.

Arithmetic operators

Python is a very good calculator. The operators:

Operator	Does	Example	Result
`+`	add	`7 + 2`	`9`
`-`	subtract	`7 - 2`	`5`
`*`	multiply	`7 * 2`	`14`
`/`	divide	`7 / 2`	`3.5`
`//`	divide and drop the remainder	`7 // 2`	`3`
`%`	remainder after dividing	`7 % 2`	`1`
`**`	to the power of	`7 ** 2`	`49`

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

Division always gives a float

/ always returns a decimal, even when the answer is whole:

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

5.0

That's usually fine. When you need a whole number, use // or int().

Whole-number division and remainder

// and % answer two everyday questions. You have ₦25,000 and data bundles cost ₦3,500: how many can you buy, and what's left?

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

7
500

Seven bundles, ₦500 change. % is also how you check whether a number is even (n % 2 == 0) or turn 130 minutes into hours and minutes:

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

2 hours and 10 minutes

The order of operations

Python follows the same order as maths: brackets first, then powers, then * / // %, then + -. When operators have the same rank, it works left to right.

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

14
20

In the first line, 3 * 4 happens first. Brackets change the order. When in doubt, add brackets: they cost nothing and make your intent clear.

A practical example. Your scores are 67, 81 and 54. The average needs brackets round the sum:

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

166.0
67.33333333333333

The first is wrong: only 54 was divided by 3.

Rounding

round(number, places) rounds to a number of decimal places. With no places, it rounds to a whole number:

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

67.33
67

Why 0.1 + 0.2 isn't exactly 0.3

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

0.30000000000000004

Computers store decimals in binary, and some decimals, like 0.1, can't be stored exactly, just as 1/3 can't be written exactly as a decimal. The error is tiny, but it shows up. Round when you display results, and never test decimals with ==.

Useful built-in functions

Function	Returns	Example	Result
`abs(x)`	the value without its sign	`abs(-500)`	`500`
`min(a, b, ...)`	the smallest	`min(67, 81, 54)`	`54`
`max(a, b, ...)`	the largest	`max(67, 81, 54)`	`81`
`round(x, n)`	x rounded to n places	`round(3.14159, 2)`	`3.14`
`pow(x, y)`	x to the power y	`pow(2, 10)`	`1024`

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

500
54 81

The math module

More maths lives in the math module, a collection of extra tools you import before using:

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

12.0
5
4
3.141592653589793

math.ceil rounds up and math.floor rounds down, whatever the decimal. That's handy for "how many buses do we need?": 130 students at 18 seats a bus needs math.ceil(130 / 18), which is 8, not 7.2.

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

Working with money

Percentages

A percentage is just multiplication by a fraction. 7.5% VAT on ₦40,000:

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

3000.0
43000.0

A 15% discount, and what share one amount is of another:

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

34000.0
20.8

So ₦12,500 is 20.8% of ₦60,000.

Formatting numbers for people

Long numbers are hard to read. Inside an f-string, add a format after a colon:

Format	Does	Example	Shows
`:,`	thousands separators	`f"{1234567:,}"`	`1,234,567`
`:.2f`	two decimal places	`f"{3.14159:.2f}"`	`3.14`
`:,.0f`	separators, no decimals	`f"{43000.0:,.0f}"`	`43,000`
`:.1%`	as a percentage	`f"{0.208:.1%}"`	`20.8%`

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

Total: ₦43,000
Share: 20.8%

When it goes wrong

print(100 / 0)

Output

ZeroDivisionError: division by zero

Dividing by zero is impossible, and Python stops. Check the divisor first, for example if count > 0:, when it could be zero.

print("100" * 2 + 50)

Output

TypeError: can only concatenate str (not "int") to str

"100" is text, so "100" * 2 is "100100", and text plus a number fails. Convert first: int("100") * 2 + 50.

Summary

You want...	Write
a division with decimals	`a / b`
how many whole times	`a // b`
what's left over	`a % b`
a power	`a ** b`
a rounded result	`round(x, 2)`
round up / down	`math.ceil(x)` / `math.floor(x)`
a percentage of a value	`value * rate / 100`
money for people	`f"₦{amount:,.0f}"`

Try it

Practice

You have ₦25,000. Data bundles cost ₦3,500 each. Using %, how much change is left after buying as many bundles as you can?

Practice

What does 2 + 3 * 4 ** 2 give? Work it out, then check in Colab.

Practice

A trip needs seats for 130 students. Each bus holds 18. How many buses do you need? Use math.ceil.

Task

8 min

Write a small shopping calculator: store a price and a quantity, work out the subtotal, add 7.5% VAT, and print the subtotal, VAT and total as naira with thousands separators using f-strings. Run it, then paste your code.

Your work is checked for

A price and a quantity in variables
Multiplies them
Works out 7.5% VAT
Prints with f-strings
Formats with thousands separators

Earn your badge

Take the module check

Questions on this module. Pass and you earn the Python Numbers badge, free.

Create a free account to earn the badge

Lesson 3 of 10

Module 3 · Python for Beginners

Numbers and Maths

Do arithmetic in Python: the operators, whole-number division and remainders, the order of operations, rounding, useful built-in functions, the math module and formatting money.

About 35 minutes

Open in ColabEvery example as a notebook you can run, edit and save to your Google Drive.

Arithmetic operators

Python is a very good calculator. The operators:

Operator	Does	Example	Result
`+`	add	`7 + 2`	`9`
`-`	subtract	`7 - 2`	`5`
`*`	multiply	`7 * 2`	`14`
`/`	divide	`7 / 2`	`3.5`
`//`	divide and drop the remainder	`7 // 2`	`3`
`%`	remainder after dividing	`7 % 2`	`1`
`**`	to the power of	`7 ** 2`	`49`

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

Division always gives a float

/ always returns a decimal, even when the answer is whole:

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

5.0

That's usually fine. When you need a whole number, use // or int().

Whole-number division and remainder

// and % answer two everyday questions. You have ₦25,000 and data bundles cost ₦3,500: how many can you buy, and what's left?

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

7
500

Seven bundles, ₦500 change. % is also how you check whether a number is even (n % 2 == 0) or turn 130 minutes into hours and minutes:

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

2 hours and 10 minutes

The order of operations

Python follows the same order as maths: brackets first, then powers, then * / // %, then + -. When operators have the same rank, it works left to right.

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

14
20

In the first line, 3 * 4 happens first. Brackets change the order. When in doubt, add brackets: they cost nothing and make your intent clear.

A practical example. Your scores are 67, 81 and 54. The average needs brackets round the sum:

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

166.0
67.33333333333333

The first is wrong: only 54 was divided by 3.

Rounding

round(number, places) rounds to a number of decimal places. With no places, it rounds to a whole number:

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

67.33
67

Why 0.1 + 0.2 isn't exactly 0.3

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

0.30000000000000004

Useful built-in functions

Function	Returns	Example	Result
`abs(x)`	the value without its sign	`abs(-500)`	`500`
`min(a, b, ...)`	the smallest	`min(67, 81, 54)`	`54`
`max(a, b, ...)`	the largest	`max(67, 81, 54)`	`81`
`round(x, n)`	x rounded to n places	`round(3.14159, 2)`	`3.14`
`pow(x, y)`	x to the power y	`pow(2, 10)`	`1024`

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

500
54 81

The math module

More maths lives in the math module, a collection of extra tools you import before using:

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

12.0
5
4
3.141592653589793

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

Working with money

Percentages

A percentage is just multiplication by a fraction. 7.5% VAT on ₦40,000:

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

3000.0
43000.0

A 15% discount, and what share one amount is of another:

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

34000.0
20.8

So ₦12,500 is 20.8% of ₦60,000.

Formatting numbers for people

Long numbers are hard to read. Inside an f-string, add a format after a colon:

Format	Does	Example	Shows
`:,`	thousands separators	`f"{1234567:,}"`	`1,234,567`
`:.2f`	two decimal places	`f"{3.14159:.2f}"`	`3.14`
`:,.0f`	separators, no decimals	`f"{43000.0:,.0f}"`	`43,000`
`:.1%`	as a percentage	`f"{0.208:.1%}"`	`20.8%`

Python · try it yourself

Edit the code and press Run (Ctrl + Enter). Examples on this page share their variables, like cells in a notebook.

Output

Total: ₦43,000
Share: 20.8%

When it goes wrong

print(100 / 0)

Output

ZeroDivisionError: division by zero

Dividing by zero is impossible, and Python stops. Check the divisor first, for example if count > 0:, when it could be zero.

print("100" * 2 + 50)

Output

TypeError: can only concatenate str (not "int") to str

"100" is text, so "100" * 2 is "100100", and text plus a number fails. Convert first: int("100") * 2 + 50.

Summary

You want...	Write
a division with decimals	`a / b`
how many whole times	`a // b`
what's left over	`a % b`
a power	`a ** b`
a rounded result	`round(x, 2)`
round up / down	`math.ceil(x)` / `math.floor(x)`
a percentage of a value	`value * rate / 100`
money for people	`f"₦{amount:,.0f}"`

Try it

Practice

You have ₦25,000. Data bundles cost ₦3,500 each. Using %, how much change is left after buying as many bundles as you can?

Practice

What does 2 + 3 * 4 ** 2 give? Work it out, then check in Colab.

Practice

A trip needs seats for 130 students. Each bus holds 18. How many buses do you need? Use math.ceil.

Task

8 min

Your work is checked for

A price and a quantity in variables
Multiplies them
Works out 7.5% VAT
Prints with f-strings
Formats with thousands separators

Earn your badge

Take the module check

Questions on this module. Pass and you earn the Python Numbers badge, free.

Create a free account to earn the badge