Explain the Python String Formatting

Explain the Python String Formatting

Python string formatting allows you to insert variables or expressions into strings dynamically — instead of concatenating manually.

There are four main ways to format strings in Python, each evolving with the language.

1. Old Style Formatting (`%` Operator)

This is similar to C’s printf formatting.

name = "Anna"
age = 25
print("My name is %s and I am %d years old." % (name, age))

Output:

My name is Anna and I am 25 years old.

Common format specifiers:

Specifier	Meaning	Example Output
`%s`	String	`'Anna'`
`%d`	Integer	`25`
`%f`	Floating-point	`25.000000`
`%.2f`	2 decimal places	`25.00`

2. `str.format()` Method (Introduced in Python 2.6+)

This method uses {} placeholders inside strings.

name = "Anna"
age = 25
print("My name is {} and I am {} years old.".format(name, age))

Output:

My name is Anna and I am 25 years old.

You can also use indexes or named arguments:

print("My name is {0} and I am {1} years old. {0} loves Python.".format(name, age))
print("My name is {name} and I am {age} years old.".format(name="Anna", age=25))

Formatting numbers:

pi = 3.1415926
print("Pi rounded to 2 decimals: {:.2f}".format(pi))

Output:

Pi rounded to 2 decimals: 3.14

3. Formatted String Literals (f-Strings) — Python 3.6+

This is the modern and most readable way.

You prefix the string with f or F, and expressions inside {} are evaluated directly.

name = "Anna"
age = 25
print(f"My name is {name} and I am {age} years old.")

Output:

My name is Anna and I am 25 years old.

You can also use expressions inside {}:

print(f"Next year, I’ll be {age + 1}.")

Number formatting:

pi = 3.1415926
print(f"Pi rounded to 3 decimals: {pi:.3f}")

Output:

Pi rounded to 3 decimals: 3.142

Alignment and width:

name = "Anna"
print(f"|{name:<10}|")  # Left align
print(f"|{name:^10}|")  # Center align
print(f"|{name:>10}|")  # Right align

Output:

|Anna      |
|   Anna   |
|      Anna|

4. Template Strings (from `string` module)

Useful when you want safe substitutions (e.g., user input).

from string import Template

t = Template("Hello, $name! You have $$${amount}.")
msg = t.substitute(name="Anna", amount=100)
print(msg)

Output:

Hello, Anna! You have $100.

If you use .safe_substitute() instead, it won’t raise an error if a placeholder is missing.

Comparison Summary

Method	Example	Best For
`%`	`"Hello %s" % name`	Legacy code
`.format()`	`"Hello {}".format(name)`	Python 2/3 compatibility
`f""`	`f"Hello {name}"`	Modern, fast, readable
`Template`	`Template("Hello $name")`	Safe user input formatting

Example Summary

name = "Anna"
age = 25
pi = 3.14159

# 1. Old Style
print("Name: %s, Age: %d" % (name, age))

# 2. str.format()
print("Name: {}, Age: {}".format(name, age))

# 3. f-String
print(f"Name: {name}, Age: {age}, Pi: {pi:.2f}")

# 4. Template
from string import Template
t = Template("Name: $name, Age: $age")
print(t.substitute(name=name, age=age))

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Explain the Python String Formatting

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1 Answers

1. Old Style Formatting (% Operator)

Common format specifiers:

2. str.format() Method (Introduced in Python 2.6+)

3. Formatted String Literals (f-Strings) — Python 3.6+

4. Template Strings (from string module)

Comparison Summary

Example Summary

1. Old Style Formatting (`%` Operator)

2. `str.format()` Method (Introduced in Python 2.6+)

4. Template Strings (from `string` module)