f-strings — Modern String Formatting

By the end of this lesson you can:

• Recognise the f prefix and drop variables into a string with {name}.
• Embed full Python expressions inside braces — {a + b}, {len(items)}, even method calls.
• Print a literal brace by typing it twice — {{ and }}.
• Choose between f-strings, commas in print() and string concatenation — and explain why f-strings usually win.

We've been writing lines like this all term:

name = "Aisyah"
age = 12
print("Hi", name, "— you are", age, "years old.")

Predict what the f-string version below prints:

print(f"Hi {name} — you are {age} years old.")

Hi Aisyah — you are 12 years old.

The shape

Add a lower-case f (or F) right before the opening quote. Anything in { } becomes Python.

name = "Wei Jie"
score = 95

msg = f"Player {name} scored {score} points!"
print(msg)
# → Player Wei Jie scored 95 points!

Without the f, the braces would print literally. The prefix is the magic switch.

Any expression goes

The braces don't just hold variable names. They hold any Python expression — maths, function calls, method calls, indexing.

a = 6
b = 7
print(f"{a} times {b} is {a * b}")
# → 6 times 7 is 42

print(f"In upper case: {name.upper()}")
# → In upper case: WEI JIE

scores = [82, 91, 76]
print(f"Class average: {sum(scores) / len(scores)}")
# → Class average: 83.0

That last one would otherwise need a separate avg = sum(...) / len(...) line. f-strings make tiny calculations feel weightless.

Multi-line f-strings

Triple-quote, then add f. Every brace inside the block becomes a window.

name = "Iman"
hp   = 50

print(f"""
═════════════════════
   Player: {name}
   HP    : {hp}
   Level : {hp // 10}
═════════════════════
""")

Great for game banners and report cards — much cleaner than four separate print lines.

Printing a literal brace

If you actually want a { or } in the output, type it twice. Python prints one.

x = 42
print(f"The answer is {x} (sometimes written as {{42}}).")
# → The answer is 42 (sometimes written as {42}).

f-string vs. comma vs. concatenation

You now know three ways to build a printed line. Read them side by side:

Style                Code                              Output
comma            print("Hi", name, "age", age)     Hi Aisyah age 12
concatenation    print("Hi " + name + " age "      Hi Aisyah age 12
                  + str(age))                       (and: TypeError if you forget str())
f-string         print(f"Hi {name} age {age}")     Hi Aisyah age 12

The f-string wins on three counts: no extra spaces sneaking in (comma puts one between every item), no str() conversions (concatenation can't mix string and number directly), and the layout reads exactly like the output line.

fruit = "apple"
print(f"I like {fruit.upper()}!")        # ✅ fine
print(f"First letter: {fruit[0]}")       # ✅ fine
print(f"Says: {'hello'}")                # ✅ inner quotes are different
# print(f"Says: {"hello"}")              # ❌ SyntaxError — same quotes

The story

Pak Cik Razif's warung needs a printed receipt for each customer. The old code used commas and looked scruffy. We'll rebuild it with f-strings and a calculation in the braces.

Save as receipt.py:

Code

# receipt.py — order summary with f-strings

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

print(f"=== Pak Cik Razif's Warung ===")
print(f"Customer: {customer}")
print()

subtotal = 0
for name, price, qty in items:
    line_total = price * qty
    subtotal += line_total
    print(f"{name}  x{qty}  RM {line_total}")

tax    = subtotal * SST
grand  = subtotal + tax

print()
print(f"Subtotal : RM {subtotal}")
print(f"SST  6%  : RM {tax}")
print(f"Grand    : RM {grand}")
print()
print(f"Thank you, {customer}! See you again.")

Output

=== Pak Cik Razif's Warung ===
Customer: Aisyah

Nasi lemak  x1  RM 8.0
Teh tarik  x2  RM 7.0
Roti planta  x1  RM 4.5

Subtotal : RM 19.5
SST  6%  : RM 1.17
Grand    : RM 20.67
Thank you, Aisyah! See you again.

Read the diff

Two patterns to spot. (1) Tuple unpacking inside the loop — for name, price, qty in items — pulls every piece of each item out by name (PY-L2-04). (2) The braces hold computed values — {price * qty} — saving a separate variable line.

An f-string is a normal string with a leading f and tiny Python windows in curly braces. Whatever you write in the braces is evaluated and dropped in — variables, maths, function calls, method calls, even conditional expressions. f-strings beat commas and concatenation because they read like the line they print, never add stray spaces, and don't need str() conversions. Double the brace ({{) to print a literal one; don't reuse the outer quote-style inside a brace.