f-string Specifiers — Width, Decimals, Padding

By the end of this lesson you can:

• Force a fixed number of decimal places with {value:.2f}.
• Set a minimum column width with {value:10}.
• Align with < (left), > (right) and ^ (centre).
• Pad numbers with leading zeros — {n:03} — for IDs like 005.
• Add a thousands separator with {n:,}.

Yesterday's receipt printed RM 8.0. Compare with this version. Predict the output:

subtotal = 19.5
tax      = 1.17
grand    = 20.67

print(f"Subtotal : RM {subtotal:.2f}")
print(f"SST  6%  : RM {tax:.2f}")
print(f"Grand    : RM {grand:.2f}")

Subtotal : RM 19.50
SST  6%  : RM 1.17
Grand    : RM 20.67

The shape

{ value : [fill][align][width][,][.precision][type] }
                            └────┬─────┘ └─┬─┘ └────┬────┘ └─┬─┘
              alignment, optional width    thousands  decimals  type
                                          separator   (.2f)    (f, d, ...)

You won't use every part on every value. The four you'll meet today are:

• .2f — "two decimal places, fixed-point".
• 10 — "minimum 10 characters wide".
• >10, <10, ^10 — width plus alignment.
• 03 — width 3, padded with leading zeros.
• , — thousands separator.

Decimal places — .2f

For money, always force two decimals. .2f means "fixed point, two digits after the dot".

pi = 3.14159265
print(f"{pi}")            # → 3.14159265
print(f"{pi:.2f}")        # → 3.14
print(f"{pi:.4f}")        # → 3.1416
print(f"{8:.2f}")         # → 8.00   (yes, even on a whole number)

Width — 10

A bare number after the colon is the minimum width. Shorter strings get padded with spaces.

print(f"|{'Aisyah':10}|")     # → |Aisyah    |    (10 chars; left by default for strings)
print(f"|{42:5}|")            # → |   42|         (5 chars; right by default for numbers)

Alignment — < > ^

Use a symbol before the width to force the alignment:

name = "Wei Jie"
print(f"|{name:<10}|")      # → |Wei Jie   |     left
print(f"|{name:>10}|")      # → |   Wei Jie|     right
print(f"|{name:^10}|")      # → | Wei Jie  |     centred

Together with .2f for money, you can finally build aligned receipts:

print(f"|{'Item':<14}|{'Price':>8}|")
print(f"|{'Nasi lemak':<14}|{8:>8.2f}|")
print(f"|{'Teh tarik':<14}|{3.5:>8.2f}|")

|Item          |   Price|
|Nasi lemak    |    8.00|
|Teh tarik     |    3.50|

Leading zeros — 03

For ID-style numbers that should always have a fixed number of digits, use 0 as the fill character:

for n in range(1, 6):
    print(f"P{n:03}")
# → P001
#   P002
#   P003
#   P004
#   P005

Thousands separator — ,

A bare comma turns a long number into 1,000,000.

big = 1234567
print(f"{big}")        # → 1234567
print(f"{big:,}")      # → 1,234,567

money = 1234.5
print(f"RM {money:,.2f}")     # → RM 1,234.50    (combine: comma + decimals)

Money (2 dp)              {value:.2f}        → 8.00
Money + thousands         {value:,.2f}       → 1,234.50
Padded ID                 {n:03}             → 007
Right-align in 8 chars    {n:>8}             → "      42"
Left-align in 10 chars    {name:<10}         → "Aisyah    "
Centred in 14 chars       {title:^14}        → "   Hello!    "
Percent (× 100, %)        {0.75:.0%}         → 75%

The story

Reopen yesterday's receipt.py. The prices were off by a decimal place and the columns drifted. Today we fix it with specifiers.

Save as receipt2.py:

Code

# receipt2.py — receipt with alignment + decimals

customer = "Aisyah"
items = [
    ("Nasi lemak",    8.00, 1),
    ("Teh tarik",     3.50, 2),
    ("Roti planta",   4.50, 1),
    ("Cendol",        5.00, 3),
]
SST = 0.06

print(f"{'PAK CIK RAZIF WARUNG':^32}")
print(f"{'Customer: ' + customer:^32}")
print("-" * 32)
print(f"{'Item':<16}{'Qty':>5}{'Total':>11}")
print("-" * 32)

subtotal = 0
for name, price, qty in items:
    line_total = price * qty
    subtotal  += line_total
    print(f"{name:<16}{qty:>5}{line_total:>11.2f}")

tax   = subtotal * SST
grand = subtotal + tax

print("-" * 32)
print(f"{'Subtotal':<21}{subtotal:>11.2f}")
print(f"{'SST 6%':<21}{tax:>11.2f}")
print(f"{'GRAND TOTAL':<21}{grand:>11.2f}")
print()
print(f"{'Thank you, ' + customer + '!':^32}")

Output

     PAK CIK RAZIF WARUNG
       Customer: Aisyah
--------------------------------
Item              Qty      Total
--------------------------------
Nasi lemak          1       8.00
Teh tarik           2       7.00
Roti planta         1       4.50
Cendol              3      15.00
--------------------------------
Subtotal                  34.50
SST 6%                     2.07
GRAND TOTAL               36.57

       Thank you, Aisyah!

Read the diff

Four specifiers in one file: :^32 centres a banner, :<16 left-aligns the item column, :>5 right-aligns the quantity, and :>11.2f right-aligns the prices with two decimals. The dashes-line "-" * 32 uses Level-1 string multiplication.

Inside an f-string brace, anything after a colon is a format specifier. .2f forces two decimal places. A bare number sets a minimum width — <, > and ^ control alignment. 03 pads numbers with leading zeros. , adds a thousands separator. Combine them — {value:>10,.2f} right-aligns a 10-wide field with thousands and 2 decimals. These specifiers are the single biggest jump from "raw output" to "polished report".