Python format() Function

The format() function in Python lets you format strings by inserting values into placeholders. It's a clean and powerful way to build strings with variables, numbers, and text.

Syntax

string.format(value1, value2, ...)

Parameters:

• value1, value2, ... – Values (strings, numbers, etc.) to insert into the string

Returns:

• A new string with placeholders replaced by the specified values.

Basic Example

name = "Alice"
age = 30
message = "My name is {} and I am {} years old.".format(name, age)
print(message)

My name is Alice and I am 30 years old.

Using Positional Indexes

msg = "The {1} comes after the {0}.".format("first", "second")
print(msg)

The second comes after the first.

Using Named Placeholders

msg = "Hello, {name}. You have {messages} new messages."
print(msg.format(name="John", messages=5))

Hello, John. You have 5 new messages.

Formatting Numbers

price = 49.5678
print("Price: {:.2f}".format(price))

Price: 49.57

{:.2f} means: round to 2 decimal places

Aligning Text

print("{:<10} | {:^10} | {:>10}".format("Left", "Center", "Right"))

Left       |   Center   |      Right

Tip: Use < for left, ^ for center, and > for right alignment.

Use Case: Create a Report

product = "Pen"
qty = 10
unit_price = 1.5
print("Item: {}, Qty: {}, Total: ${:.2f}".format(product, qty, qty * unit_price))

Item: Pen, Qty: 10, Total: $15.00

Common Mistakes

• Using incorrect number of placeholders vs values – will raise an IndexError
• Using invalid format specifiers like {:abc}

Interview Tip

String formatting is frequently asked in Python coding rounds. The format() function is a powerful alternative to string concatenation.

Summary

• format() inserts values into a string using placeholders {}
• Supports positional and named arguments
• Useful for formatting numbers, aligning text, and generating clean output

Practice Problem

Write a program to print: “Hello, my name is NAME and I scored SCORE% in Python.” using the format() function.

name = "Rahul"
score = 93.5
print("Hello, my name is {} and I scored {}% in Python.".format(name, score))