Format Specifiers in Python

Python provides format specifiers for formatting strings, numbers, and other data types. These specifiers can be used with f-strings (f""), the format() method, or % formatting.

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1. Integer Formatting

Format	Description	Example
%d or {}	Integer (decimal)	print(f"{100:d}") → 100
%o or {:#o}	Octal representation	print(f"{100:o}") → 144
%x or {:#x}	Hexadecimal (lowercase)	print(f"{100:x}") → 64
%X or {:#X}	Hexadecimal (uppercase)	print(f"{100:X}") → 64
%b or {:#b}	Binary representation	print(f"{100:b}") → 1100100

Examples

num = 100
print(f"Decimal: {num:d}")
print(f"Binary: {num:b}")
print(f"Octal: {num:o}")
print(f"Hexadecimal: {num:X}")

Output:

Decimal: 100
Binary: 1100100
Octal: 144
Hexadecimal: 64

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2. Floating-Point Formatting

Format	Description	Example
%f or {:.nf}	Floating point with n decimal places	print(f"{3.14159:.2f}") → 3.14
%e or {:.ne}	Scientific notation (lowercase)	print(f"{3.14159:.2e}") → 3.14e+00
%E or {:.nE}	Scientific notation (uppercase)	print(f"{3.14159:.2E}") → 3.14E+00
%g or {:.ng}	Auto chooses %f or %e based on value	print(f"{3.14159:.3g}") → 3.14

Examples

pi = 3.14159265358979
print(f"Default: {pi}")
print(f"2 Decimal Places: {pi:.2f}")
print(f"Scientific Notation: {pi:.2e}")
print(f"Compact: {pi:.3g}")

Output:

Default: 3.14159265358979
2 Decimal Places: 3.14
Scientific Notation: 3.14e+00
Compact: 3.14

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3. String Formatting

Format	Description	Example
%s or {}	String	print(f"{'Python'}") → Python
%r or {!r}	Raw string (repr)	print(f"{'Hello!':!r}") → 'Hello!'
%c	Character from ASCII	print(f"{65:c}") → A

Examples

text = "Hello"
print(f"Normal: {text}")
print(f"Repr: {text!r}")
print(f"ASCII Character: {65:c}")

Output:

Normal: Hello
Repr: 'Hello'
ASCII Character: A

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4. Aligning and Padding

Format	Description	Example
{:<n}	Left-align	print(f"{'Hi':<10}") → 'Hi '
{:>n}	Right-align	print(f"{'Hi':>10}") → ' Hi'
{:^n}	Center-align	print(f"{'Hi':^10}") → ' Hi '
{:0n}	Zero-padding	print(f"{42:05}") → 00042

Examples

name = "Python"
print(f"Left: {name:<10}-End")
print(f"Right: {name:>10}-End")
print(f"Center: {name:^10}-End")
print(f"Zero-Padded: {42:05}")

Output:

Left: Python    -End
Right:     Python-End
Center:   Python  -End
Zero-Padded: 00042

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5. Percentage Formatting

Format	Description	Example
%	Converts to percentage	print(f"{0.85:.0%}") → 85%

Example

discount = 0.25
print(f"Discount: {discount:.0%}")

Output:

Discount: 25%

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6. Comma Separators for Large Numbers

Format	Description	Example
:,	Adds comma separators	print(f"{1000000:,}") → 1,000,000

Example

big_number = 1000000
print(f"Formatted Number: {big_number:,}")

Output:

Formatted Number: 1,000,000

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7. Custom Number Base Formatting

Format	Description	Example
{:#b}	Binary with 0b prefix	print(f"{10:#b}") → 0b1010
{:#o}	Octal with 0o prefix	print(f"{10:#o}") → 0o12
{:#x}	Hexadecimal with 0x prefix	print(f"{10:#x}") → 0xa

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Conclusion

Python format specifiers enhance readability and make data representation flexible. Mastering them is crucial for clean, readable code! 🚀