Python f-strings explained with examples

An f-string is a string with an f before the opening quote. Anything inside {} is worked out by Python and put into the text, so you can drop in variables and even calculations.

Example: a receipt line

item = "mug"
price = 8.50
quantity = 3

print(f"{quantity} x {item} at {price} each")
print(f"Total: {price * quantity}")
print(f"Total: {price * quantity:.2f}")
print(f"{item.upper()} costs ${price:.2f}")

Output:

3 x mug at 8.5 each
Total: 25.5
Total: 25.50
MUG costs $8.50

How it works

• The f before the quote turns the string into an f-string. Without it, the braces are just text.
• {quantity} and {item} are replaced by the values of those variables.
• Inside the braces you can write any expression, like price * quantity or item.upper(). Python calculates it first, then inserts the result.
• :.2f after the expression is a format. It shows a number with exactly 2 digits after the decimal point, so 25.5 becomes 25.50. This is handy for money.
• The $ in the last line is plain text. Only {} is special.

You can use f-strings with numbers and text alike. Python converts the value to a string for you, so you don't need str(). That is why they are easier to read than joining pieces with +, where a number would need str() first.

Common mistakes

Forgetting the f. The braces then print literally:

price = 8.50
print("Total: {price}")

Output:

Total: {price}

Fix: write print(f"Total: {price}").

Forgetting the braces. Names outside {} are just text:

print(f"Total: price * quantity")

This prints Total: price * quantity. Fix: put the expression inside braces, like f"Total: {price * quantity}".

Takeaway

Put f before the quote, put variables or expressions in {}, and add :.2f when you want a price with two decimals.