Strings in Python are immutable, meaning they can't be changed after they're created. But don’t worry — you can modify a string by creating a new string using Python’s built-in string methods.

This tutorial shows you how to modify strings using methods like upper(), lower(), replace(), strip(), and more.

Strings are Immutable in Python

You can’t change the characters in a string directly:

txt = "hello"
# txt[0] = "H"  # ❌ This will raise an error

Instead, you create a new string using methods:

txt = "hello"
txt = txt.capitalize()
print(txt)  # Output: Hello

Common String Modification Methods

1. upper() – Convert to Uppercase

txt = "python"
print(txt.upper())  # Output: PYTHON

  2. lower() – Convert to Lowercase

txt = "PYTHON"
print(txt.lower())  # Output: python

3. strip() – Remove Leading and Trailing Whitespace

txt = "  Hello World  "
print(txt.strip())  # Output: Hello World

 4. replace() – Replace Substrings

txt = "I like Java"
print(txt.replace("Java", "Python"))  # Output: I like Python

 5. split() – Split String into a List

txt = "apple,banana,cherry"
fruits = txt.split(",")
print(fruits)  # Output: ['apple', 'banana', 'cherry']

6. join() – Join List into a String

words = ['Learn', 'Python']
result = " ".join(words)
print(result)  # Output: Learn Python

7. capitalize() – Capitalize First Letter

txt = "hello world"
print(txt.capitalize())  # Output: Hello world

8. title() – Capitalize First Letter of Every Word

txt = "python string methods"
print(txt.title())  # Output: Python String Methods

9. find() – Find Substring Index

txt = "Learn Python"
print(txt.find("Python"))  # Output: 6

Real-World Example

Example: Clean up and format user input

user_input = "   jOhN doE   "
cleaned = user_input.strip().title()
print(cleaned)  # Output: John Doe

 Summary Table of Common Methods