How to Format Numbers in Python f-Strings Easily

Use f"{value:format_spec}" to format numbers in Python f-strings. The format_spec controls decimal places, padding, alignment, and more, like .2f for two decimals or , for thousand separators.

Syntax

The basic syntax to format numbers in an f-string is f"{value:format_spec}". Here, value is the number you want to format, and format_spec defines how the number appears.

• Decimal places: Use .nf where n is the number of decimals (e.g., .2f for two decimals).
• Thousands separator: Use , to add commas (e.g., ,).
• Padding and alignment: Use width and alignment symbols like 10 for width, < for left-align, > for right-align.

python

value = 1234.5678
formatted = f"{value:,.2f}"
print(formatted)

Output

1,234.57

Example

This example shows formatting a float number with two decimal places and a comma as a thousands separator.

python

price = 1234567.89123
formatted_price = f"${price:,.2f}"
print(formatted_price)

Output

$1,234,567.89

Common Pitfalls

Common mistakes include forgetting the colon : before the format specifier or using incorrect format codes that cause errors.

Also, using f"{value:.2}" without specifying f for float formatting will not limit decimals.

python

# Wrong: missing colon
value = 123.456
# print(f"{value.2f}")  # SyntaxError

# Correct:
print(f"{value:.2f}")  # prints 123.46

Output

123.46

Quick Reference

Format Specifier	Description	Example
.2f	Two decimal places float	f"{3.14159:.2f}" → 3.14
,	Thousands separator	f"{1000000:,}" → 1,000,000
10	Width 10, right aligned	f"{42:10}" → ' 42'
<10	Width 10, left aligned	f"{42:<10}" → '42 '
^10	Width 10, centered	f"{42:^10}" → ' 42 '
e	Scientific notation	f"{1000:e}" → 1.000000e+03

Key Takeaways

Use f-strings with a colon and format specifier to control number formatting.

Common format specs include .nf for decimals, , for thousands separator, and width/alignment symbols.

Always include the colon before the format specifier to avoid syntax errors.

Test formatting with print to see the exact output before using in your program.

Use the quick reference table to remember common format specifiers.