f-strings: Building Text from Values

Why this matters

Programs constantly build sentences out of values: receipts, messages, reports. Gluing text together with + and str() gets messy fast. f-strings are the modern, readable way.

The idea

Put an f in front of the opening quote, and write any variable or calculation inside { }:

name = "Ada"
age = 36
print(f"{name} is {age} years old")        # Ada is 36 years old
print(f"Next year: {age + 1}")              # Next year: 37

Everything in the braces is evaluated, so you do not need str().

You can also control how a value is shown by adding a format specifier after a colon:

price = 2.5
print(f"{price:.2f}")        # 2.50   (exactly 2 decimal places)
print(f"{1234567:,}")        # 1,234,567   (thousands separators)
print(f"{0.256:.0%}")        # 26%   (as a percentage)

.2f is the one you will use most: “a float with 2 digits after the point”. Handy for money. A literal dollar sign needs no special treatment: f"${price:.2f}" prints $2.50.

Try it

Make a few f-strings of your own: print a sentence with your name and a calculation inside it, and format a number with :.1f, :.2f and :,.

Your turn

The starter reads an item name, a price per item and a quantity. Print one receipt line. For Coffee, 2.5 and 3 it must print exactly:

3 x Coffee at $2.50 = $7.50

Use a single f-string. Type the three inputs (one per line) in the Input box to try it.

Recap

• f"text {value}" puts values straight into text.
• Anything can go inside the braces, including calculations.
• {x:.2f} shows a float with two decimals.

Common mistakes

• Forgetting the f: without it, Python prints the braces literally.
• Quotes inside the braces: if your f-string uses double quotes, use single quotes for anything inside it (and vice versa).
• Rounding when you meant to format: :.2f only changes how the number is shown, which is what you want for display.