Case Conversion Methods

Learning roadmap

You'll learn these five methods in the same order they're commonly used.

Syntax pattern (applies to every method)

s = "python"

s.upper()
s.lower()
s.title()

Remember: object.method() → returns a new string.

1. capitalize()

Capitalizes only the first character of the entire sentence.

s = "python is an oop lang"

print(s.capitalize())
# Python is an oop lang

Store the result:

s = s.capitalize()

Memory: One sentence → one capital.

2. title()

Capitalizes the first letter of every word.

s = "python is an oop lang"

print(s.title())
# Python Is An Oop Lang

Memory: Every word gets a title.

capitalize() vs title()

This is the most common interview question.

Method	Result
capitalize()	Python is an oop lang
title()	Python Is An Oop Lang

3. upper()

Converts every letter to uppercase.

s = "python"

print(s.upper())
# PYTHON

Digits and symbols stay unchanged:

print("abc123".upper())
# ABC123

4. lower()

Converts every letter to lowercase.

s = "Data Science"

print(s.lower())
# data science

Real-world example:

email = "USER@GMAIL.COM"
email = email.lower()

5. swapcase()

Swaps uppercase ↔ lowercase.

s = "PyThOn"

print(s.swapcase())
# pYtHoN

Numbers remain unchanged:

print("12345".swapcase())
# 12345

Immutability reminder

Methods create a new string. The original stays unchanged until you reassign.

Without reassignment:

s = "python"

s.upper()

print(s)
# python

With reassignment:

s = s.upper()

print(s)
# PYTHON

Playground example

s = "python is an oop lang"

print("capitalize:", s.capitalize())
print("title:", s.title())
print("upper:", s.upper())
print("lower:", s.lower())
print("swapcase:", "PyThOn".swapcase())

Expected output:

capitalize: Python is an oop lang
title: Python Is An Oop Lang
upper: PYTHON IS AN OOP LANG
lower: python is an oop lang
swapcase: pYtHoN

Use the lesson playground at the bottom of the page to run this code live.

Method summary

Method	Effect	Memory
capitalize()	First character uppercase	One sentence
title()	Every word uppercase	Book title
upper()	All letters uppercase	Everything UP
lower()	All letters lowercase	Everything down
swapcase()	Flip letter casing	Reverse

Quick knowledge check

1. Which method title-cases every word?
   Answer: title()

2. After s.upper(), is s changed?
   Answer: No. Only if you assign: s = s.upper()

3. What happens to digits in swapcase()?
   Answer: They remain unchanged.

30-second visual revision

Interview shortcut: One → capitalize() · Every → title() · All BIG → upper() · All small → lower() · Flip → swapcase()

Next: String Validation Methods.