Python f-string Formatting: Width, Align, Commas

Give a Value a Width in an f-string

In an f-string, a colon and a number after the value set its width: the smallest number of characters it takes up. Python fills the rest with spaces. {name:10} means "give name 10 characters of room".

Think of it like the boxes on a paper form: every box is the same size, whether you write a short name or a long one in it.

1234name = "Sunny"
score = 42
print(f"[{name:10}]")
print(f"[{score:6}]")

The square brackets are only there so you can see the spaces.

The rules

• {value:10} makes the value at least 10 characters wide.
• By default, text sits on the left and numbers sit on the right.
• A value that is too long is never cut. It simply sticks out.
• The colon is the same one you used for :.2f in chapter 5. Everything after it says how to show the value.

12name = "Rocky"
print(f"[{name:3}]")

Why widths are useful: columns

Give every row the same widths, and the columns line up by themselves:

1234items = ["Tea", "Sandwich", "Cake"]
prices = [20, 150, 80]
for i in range(len(items)):
    print(f"{items[i]:10}{prices[i]:5}")

Without widths, the prices would start at a different place on every line.

Common beginner doubt: "Is the width the number of spaces added?" No, it's the total size of the box. "Sunny" has 5 characters, so {name:10} adds 5 spaces to fill 10.

{value:10} gives a value 10 characters of room: text sits left, numbers sit right.

Align Text Left, Right or Centre

Put an alignment sign right before the width to choose where the value sits in its box: < for left, > for right and ^ for centre.

Think of it like the three align buttons in a word processor: the text is the same, only its place on the line changes.

1234name = "Lucky"
print(f"[{name:<9}]")
print(f"[{name:>9}]")
print(f"[{name:^9}]")

The rules

• The sign comes after the colon and before the width.
• A character before the sign is the fill: it's used instead of spaces.
• When the centre can't be exact, the extra space goes on the right.

Fill characters make banners

1234title = "Menu"
print(f"{title:*^14}")
print(f"{title:-<14}")
print(f"{title:.>14}")

Avoid: forgetting the colon

12name = "Lucky"
print(f"[{name>9}]")

Without the colon, Python reads name>9 as a comparison: "is name greater than 9?" And text can't be compared with a number. The colon is what starts the formatting part.

Common beginner doubt: "When should I use which?" Left for words, right for numbers (so the digits line up), and centre for titles and headings.

Write < for left, > for right and ^ for centre, right before the width.

Format Numbers: Decimals, Commas and Percent

After the colon, you can also tell Python how to write a number: how many decimals, whether to add thousands commas, or to show it as a percent. You already know :.2f from chapter 5. Now you can add more.

Think of it like a bank statement: every amount has commas and exactly two decimals, so you can read big numbers at a glance.

123456price = 1234567.891
print(f"{price:.2f}")
print(f"{price:,}")
print(f"{price:,.2f}")
population = 1400000000
print(f"{population:,}")

The rules

The order is always: alignment, width, comma, then the decimals. Read {x:>10,.2f} as "on the right, 10 wide, with commas, 2 decimals".

Percent

% multiplies by 100 for you, so store the share as a decimal:

123score = 0.875
print(f"{score:.1%}")
print(f"{score:.0%}")

A column of amounts

Width plus commas plus decimals lines up the decimal points:

123amounts = [5, 250.5, 12000]
for a in amounts:
    print(f"Rs.{a:>10,.2f}")

Avoid: number formats on text

12price = input()
print(f"{price:,.2f}")

input() gives the text "1500", and the f format (a float with decimals) only works on numbers. Convert first with float(input()).

Common beginner doubt: "Does :.2f change the number?" No. It only changes how it's shown. The variable still holds every decimal.

, adds thousands commas, .2f fixes two decimals, and a width lines them up: {x:>10,.2f}.

Print a Neat Table with f-strings

Widths, alignment and number formats come together in a table: a header row, a line, and one row per item, all with the same column widths.

Think of it like a school timetable: every column starts at the same place on every line, so your eye can run straight down it.

123456names = ["Sunny", "Rocky", "Lucky"]
marks = [92.5, 78, 100]
print(f"{'Name':<8}{'Marks':>8}")
print("-" * 16)
for i in range(len(names)):
    print(f"{names[i]:<8}{marks[i]:>8.1f}")

The header uses text in quotes inside the brackets, 'Name', with single quotes, because the f-string itself uses double quotes.

The rules

• Use the same width for a column in the header and in every row.
• Text columns go left (<), number columns go right (>), so the digits line up.
• Add up the widths to know how long the line should be: 8 + 8 is 16, so "-" * 16.
• Give every number in a column the same decimals, like .1f, so the points line up too.

A bill with a total

Keep a running total in the loop (chapter 10), then print it in the same columns:

12345678items = ["Pen", "Notebook"]
prices = [12.5, 60]
total = 0
for i in range(len(items)):
    print(f"{items[i]:<10}{prices[i]:>8.2f}")
    total += prices[i]
print("-" * 18)
print(f"{'Total':<10}{total:>8.2f}")

Common beginner doubt: "Why not use tabs, \t, from chapter 2?" A tab jumps to the next fixed stop, so one long name pushes its whole row out of line. A width is exact: the column always starts in the same place.

Same widths on every row, text on the left, numbers on the right: that's a neat table.

Practice: Formatting

Solve these to lock in what you learned in this topic. Each one runs in your browser.

1. 107.Python Program to Format a Number with CommasEasySolve
2. 108.Python Program to Print a Multiplication Table in ColumnsMediumSolve
3. 109.Python Program to Print a Neat Bill from Input LinesHardSolve