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Format Strings

String formatting in Python is used to insert variables and expressions inside strings in a clean and readable way. It helps create dynamic output messages without complex concatenation.
Python provides multiple methods for formatting strings, from basic to modern.

What Is String Formatting?

String formatting allows you to:
  • Combine text and variables
  • Display values inside strings
  • Control output format
Definition

String formatting is the process of embedding values inside a string.

Format Strings Using f-Strings (Recommended)

f-strings are the modern and most preferred way to format strings in Python. They were introduced in Python 3.6.

Syntax

python
f"string {variable}"

Code Example 1: Basic f-string

python
name = "Python"
print(f"Welcome to {name}")

Code Example 2: Multiple Variables

python
name = "John"
age = 25
print(f"Name: {name}, Age: {age}")

Code Example 3: Expression Inside f-string

python
a = 10
b = 20
print(f"Sum is {a + b}")
Best Practice

Always use f-strings for clean and readable formatting.

Format Strings Using format() Method

The format() method is an older but still valid way to format strings.

Code Example 1: Single Placeholder

python
name = "Python"
print("Welcome to {}".format(name))

Code Example 2: Multiple Placeholders

python
name = "John"
age = 30
print("Name: {}, Age: {}".format(name, age))

Code Example 3: Indexed Placeholders

python
print("{1} is learning {0}".format("Python", "John"))

Format Strings Using Named Placeholders

You can use named placeholders with the format() method.
python
print("Name: {name}, Age: {age}".format(name="Alice", age=28))
python
print("Course: {course}".format(course="AWS"))
python
print("{lang} is easy".format(lang="Python"))

Old Style Formatting (% Operator)

This is the oldest method of string formatting in Python. It is still supported but not recommended for new code.

Code Example 1: String Formatting

python
name = "Python"
print("Welcome to %s" % name)

Code Example 2: Integer Formatting

python
age = 25
print("Age is %d" % age)

Code Example 3: Multiple Values

python
name = "John"
age = 30
print("Name: %s, Age: %d" % (name, age))
Note

Avoid % formatting in modern Python code.

Formatting Numbers in Strings

Python allows formatting numbers easily.

Code Example 1: Decimal Places

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

Code Example 2: Padding Numbers

python
num = 5
print(f"Value is {num:03}")

Code Example 3: Percentage Format

python
value = 0.85
print(f"Success rate: {value:.0%}")

Multiline Format Strings

f-strings work perfectly with multi-line strings.
python
name = "Python"
version = 3

print(f"""
Language: {name}
Version: {version}
Status: Active
""")

Common Mistakes

Mixing + Instead of Formatting

python
age = 20
print("Age is " + str(age))
Better approach:
python
print(f"Age is {age}")

Summary

  • String formatting inserts values into strings
  • f-strings are the best and modern approach
  • format() is an alternative method
  • % formatting is outdated
  • Formatting improves readability and flexibility

Exercise

  • Format your name and age using f-string
  • Print sum of two numbers inside a string
  • Format a float value to 2 decimal places