Explain the Python String Formatting

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ICSM · Answer

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:andlt;10}|")  # Left align
print(f"|{name:^10}|")  # Center align
print(f"|{name:andgt;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))

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

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

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Explain the Python String Formatting

Anubhav Kumar

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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

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