Formatting Numbers

Formatting Numbers

In this tutorial, we'll display decimals, money-like values, and percentages neatly.

F-strings can also control how numbers appear.

This is especially useful for decimals:

price = 4.999
print(f"Price: {price}")

Output:

Price: 4.999

You may want two decimal places instead.

Decimal Places

Use :.2f for two decimal places:

price = 4.999
print(f"Price: {price:.2f}")

Output:

Price: 5.00

The f means fixed-point number. The .2 means two decimal places.

Money-Like Output

price = 12.5
quantity = 3
total = price * quantity

print(f"Total: £{total:.2f}")

Output:

Total: £37.50

Percentages

Use :.1% to display a decimal as a percentage:

success_rate = 0.875
print(f"Success: {success_rate:.1%}")

Output:

Success: 87.5%

Common Mistake

Formatting changes how a number is displayed. It does not change the original value:

number = 3.14159
print(f"{number:.2f}")
print(number)

The second print still shows the original number.

Store the Formatted Text

If you need the formatted version later, store it in a variable:

price = 4.5
display_price = f"£{price:.2f}"

print(display_price)

display_price is now a string. Use it for showing output, not for further maths.

Practice

Create a subtotal and tax rate. Print the tax and total with two decimal places.