Python Tutorials

Choose a lesson to begin

Hello World and Print Statements
Learn the basics of printing output in Python
Beginner
Variables and Data Types
Store and work with different types of data
Beginner
Math and Arithmetic
Perform calculations and mathematical operations
Beginner
F-Strings and Formatting
Format text output with embedded variables
Beginner
String Methods
Transform and manipulate text with built-in methods
Beginner
Lists and For Loops
Store multiple items and iterate through them
Beginner
List Comprehensions and Generator Expressions
Master concise, Pythonic ways to create and transform sequences
Intermediate
Dictionaries and Advanced Data Structures
Master key-value mappings, nested structures, and efficient data organization
Intermediate
Functions, Decorators, and Functional Programming
Write reusable code with functions, decorators, lambda expressions, and functional patterns
Intermediate
Object-Oriented Programming (OOP)
Master classes, objects, inheritance, and OOP design patterns
Advanced
Error Handling and Exceptions
Handle errors gracefully with try-except, custom exceptions, and error recovery
Intermediate
File I/O and Data Persistence
Read and write files, work with JSON/CSV, and persist application data
Advanced

String Methods

Strings in Python come with built-in methods that let you transform and manipulate text. Think of them as tools for working with words!

What Are Methods?

Methods are functions that belong to a specific data type. For strings, you use a dot (.) after the variable name:

text = "hello"
result = text.upper()

Case Conversion

.upper() - Make Uppercase

message = "hello"
print(message.upper())  # HELLO

.lower() - Make Lowercase

message = "HELLO"
print(message.lower())  # hello

Use case: Comparing user input 

answer = "YES"
if answer.lower() == "yes":
    print("You said yes!")

Text Replacement

.replace(old, new) - Replace Text

sentence = "I love fish"
new_sentence = sentence.replace("fish", "cats")
print(new_sentence)  # I love cats

Important: .replace() creates a new string, it doesn't change the original:

message = "Hello World"
new_message = message.replace("World", "Python")
print(message)      # Hello World (unchanged!)
print(new_message)  # Hello Python (new string!)

Whitespace Removal

.strip() - Remove Leading/Trailing Spaces

messy = "   hello   "
clean = messy.strip()
print(clean)  # hello

Real use: Cleaning user input 

username = input("Enter username: ")
username = username.strip()  # Remove accidental spaces
print(username)

Chaining Methods

You can use multiple methods in sequence:

text = "  python  "
result = text.strip().upper()
print(result)  # PYTHON

How it works:

  • text.strip() → "python"
  • "python".upper() → "PYTHON"

    • Real-World Examples

    Clean and Format User Input

    name = "  Alice SMITH  "
clean_name = name.strip().lower()
print(f"Welcome, {clean_name}!")

    Fix Capitalization

    city = "copenhagen"
proper_city = city.upper()
print(proper_city)  # COPENHAGEN

    Search and Replace

    template = "Hello NAME, welcome to CITY!"
personalized = template.replace("NAME", "Vidar")
personalized = personalized.replace("CITY", "Copenhagen")
print(personalized) # Hello Vidar, welcome to Copenhagen!

    Clean File Names

    filename = "My Document.txt"
clean_filename = filename.replace(" ", "_").lower()
print(clean_filename)  # my_document.txt

    Common Patterns

    Normalize text for comparison: 

    user_input = "  YES  "
if user_input.strip().lower() == "yes":
    print("Confirmed!")

    Format display text: 

    product = "laptop computer"
display = product.upper()
print(f"Product: {display}")

    Clean and validate: 

    email = "  User@Example.COM  "
clean_email = email.strip().lower()
print(f"Email: {clean_email}")

    Method Reference

    | Method | What It Does | Example | |--------|-------------|---------| | .upper() | ALL CAPS | "hi".upper() → "HI" | | .lower() | all lowercase | "HI".lower() → "hi" | | .strip() | Remove spaces from ends | " hi ".strip() → "hi" | | .replace(old, new) | Replace text | "hi".replace("h", "b") → "bi" |

    Try It Out!

  • Create a message and convert it to uppercase
  • Take a sentence and replace one word with another
  • Clean up messy input: " PYTHON " → "python"
  • Chain methods: take " hello world " and make it "HELLO WORLD"
  • Create a mad-libs style program using .replace()

    • Important Notes

    Next Steps

    Ready to work with collections of data? Learn about Lists and For Loops next!

    🐍 Python Runner