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03. Advanced String Formatting

Python provides several ways to format strings, from the old % operator to the modern f-strings. Mastering these will make your code more readable and flexible.

The Old Way: % Formatting​

name = "Alice"
age = 30
print("Hello, %s. You are %d years old." % (name, age))

str.format()​

print("Hello, {}. You are {} years old.".format(name, age))
print("Hello, {0}. You are {1} years old.".format(name, age))
print("Hello, {n}. You are {a} years old.".format(n=name, a=age))

f-Strings (Python 3.6+)​

print(f"Hello, {name}. You are {age} years old.")
print(f"Next year, you will be {age + 1}.")

Formatting Numbers​

pi = 3.14159265
print(f"Pi rounded to 2 decimals: {pi:.2f}")
print(f"As percentage: {0.25:.0%}")

Alignment and Width​

for n in [1, 10, 100]:
    print(f"{n:>5}")   # right aligned
    print(f"{n:<5}")   # left aligned

Practice Challenge​

Format a table with names and scores neatly aligned using f-strings.

students = {"Alice": 90, "Bob": 85, "Charlie": 92}

Wrap-Up​

  • Use f-strings when possible; they are concise and powerful.
  • Remember format specifiers (:.2f, :>5) for numbers and alignment.