Concatenation & Formatting (f-string, format, %)0%
Escape Characters

Concatenation & Formatting (f-string, format, %)

Beginner9 min read•Updated: 2026-09-03
Study Materials

Concatenation & Formatting (f-string, format, %)

f-strings (Formatted String Literals) are the gold standard for formatting dynamic data into text.

Key Concepts & Detailed Explanation

Evolution of Python string formatting:

  1. 1
    % formatting (Python 2 legacy): "%s is %d years old" % (name, age)
  2. 2
    str.format() (Python 3.0): "{} is {} years old".format(name, age)
  3. 3
    f-strings (Python 3.6+): f"{name} is {age} years old"

f-strings evaluate expressions at runtime and support format specifiers like {val:.2f} for decimal rounding.

Code Examples & Output

Python
product = "Keyboard"
price = 1299.856
 
# f-string with precision formatting
print(f"Item: {product}")
print(f"Price: ₹{price:.2f}")
print(f"With 18% GST: ₹{price * 1.18:.2f}")
 
# Alignment formatting
print(f"{'Header':^20}")

Expected Output:

Output
Item: Keyboard
Price: ₹1299.86
With 18% GST: ₹1533.83
Header

Best Practices & Common Pitfalls

f-strings are not only cleaner to read; they are also significantly faster than format() and % operators.

Practice Quiz

1. Which format specifier rounds a float to 2 decimal places in an f-string?

  • A) :.2d
  • B) :.2f
  • C) :%2
  • D) :round(2)
Answer: B Explanation: :.2f formats a float with 2 decimal places.

2. Can you call functions inside f-string curly braces { }?

  • A) No
  • B) Yes, any valid Python expression is supported
  • C) Only built-in math functions
  • D) Only in Python 3.12+
Answer: B Explanation: f-strings can call functions and evaluate arbitrary expressions inside { }.

Practice Challenge

Create a formatted receipt string showing Item Name, Unit Price, Quantity, and Total Amount using f-strings.

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