My Python f-string Cheatsheet

I always keep googling Python f-string formatting options, so I finally decided to put everything I actually use into one place. And what better place than my own blog?

This is my personal cheatsheet: the stuff I reach for over and over when writing real code. It’s not exhaustive, because I don’t care about every edge case or obscure format. It’s just the 80/20 of f-string formatting: the things that save me time, make code more readable, and keep me from typing “python f-string format decimal” into Google for the hundredth time.

If you also find yourself constantly forgetting whether it’s :.2f or :,.2f or :2SQPDOIFHSQDOF, this might be useful to you too.

Numbers

We’re going to use these as examples:

n = 1234567
x = 3.14159

Decimal int

f"{n:d}" → 1234567

Zero-padded width

f"{n:08d}" → 01234567

Thousands separator

Comma: f"{n:,}" → 1,234,567

Underscore: f"{n:_}" → 1_234_567

Hex / binary / octal

f"{42:x}" → 2a

f"{42:#x}" → 0x2a

f"{42:b}" → 101010

Fixed decimals

f"{x:.2f}" → 3.14

Scientific notation

f"{x:.3e}" → 3.142e+00

General format (auto picks fixed or sci)

f"{1000000:.3g}" → 1e+06

Percent

f"{0.1234:.1%}" → 12.3%

Width, Alignment, Padding

s = "hi"

Align text

Left: f"{s:<10}" → ‘hi ’

Right: f"{s:>10}" → ’ hi’

Center: f"{s:^10}" → ’ hi ‘

Fill character

f"{s:.<10}" → ‘hi…’

Sign handling

Always: f"{7:+d}" → +7

Space: f"{7: d}" → ’ 7’

Zero-pad after sign: f"{7:=+6d}" → +00007

Alternate form

f"{10:#b}" → 0b1010

f"{3.0:#.0f}" → 3. (forces decimal point)

Strings & Misc

Truncate string

f"{'abcdef':.5}" → ‘abcde’

Conversions

f"{obj!r}" → uses repr(obj)

f"{obj!s}" → uses str(obj)

f"{obj!a}" → ASCII-safe

Debug print

value = 42

f"{value=}" → “value=42”

Rounding (Banker’s Rounding)

Python’s formatting and round() both use round half to even (a.k.a. banker’s rounding):

round(2.5)  # 2
round(3.5)  # 4
 
f"{2.5:.0f}"  # '2'
f"{3.5:.0f}"  # '4'

For exact decimal rounding (finance, money): use Decimal:

from decimal import Decimal, ROUND_HALF_EVEN
Decimal("2.675").quantize(Decimal("0.01"), rounding=ROUND_HALF_EVEN)  # '2.68'

Format Spec Syntax

[[fill]align][sign][#][0][width][grouping][.precision][type]

align: < left, > right, ^ center, = pad after sign

sign: +, -, or (space)

grouping: , or _

types (common):

d int
b/o/x/X binary/octal/hex
f fixed-point
e/E scientific
g/G general
% percentage
s string

My most-used combos

Money-ish: f"{x:,.2f}" → 1,234.57
Zero-padded IDs: f"{n:08d}" → 00001234
Right-align columns: f"{s:>12}"
Hex with prefix: f"{n:#x}" → 0x2a
Percent: f"{p:.1%}" → 12.3%

Table of Contents