Chapter 13: String Methods¶

🚀 Open Notebook¶

📺 Video Tutorial¶

String methods in Python are easy! 〰️ (12:14)

📚 What You’ll Learn¶

Master Python’s powerful string manipulation methods to transform and analyze text!

🎯 Learning Objectives¶

Use common string methods (.upper(), .lower(), .title(), etc.)
Find and replace substrings
Validate string content
Combine multiple string operations

📖 Concept Explanation¶

Strings in Python come with many built-in methods for manipulation. Methods are functions that belong to an object (in this case, strings).

Common String Methods¶

Method	Description	Example
`.upper()`	Convert to uppercase	`"hello".upper()` → `"HELLO"`
`.lower()`	Convert to lowercase	`"HELLO".lower()` → `"hello"`
`.title()`	Capitalize first letter of each word	`"hello world".title()` → `"Hello World"`
`.capitalize()`	Capitalize first letter only	`"hello world".capitalize()` → `"Hello world"`
`.find()`	Find substring index	`"hello".find("e")` → `1`
`.replace()`	Replace substring	`"hello".replace("l", "L")` → `"heLLo"`
`.isdigit()`	Check if all digits	`"123".isdigit()` → `True`
`.isalpha()`	Check if all letters	`"abc".isalpha()` → `True"`
`.strip()`	Remove whitespace	`" hi ".strip()` → `"hi"`
`.split()`	Split into list	`"a,b,c".split(",")` → `['a','b','c']`

💡 Examples¶

Example 1: Case Conversion¶

name = "john DOE"
print(name.upper())      # JOHN DOE
print(name.lower())      # john doe
print(name.title())      # John Doe
print(name.capitalize()) # John doe

Example 2: Finding Substrings¶

text = "Python Programming"
print(text.find("Pro"))      # 7 (index where "Pro" starts)
print(text.find("Java"))     # -1 (not found)
print("Pro" in text)         # True (membership check)

Example 3: Replacing Text¶

phone = "123-456-7890"
clean = phone.replace("-", "")
print(clean)  # 1234567890

message = "Hello World"
new_msg = message.replace("World", "Python")
print(new_msg)  # Hello Python

Example 4: Validation¶

user_input = "12345"
if user_input.isdigit():
    number = int(user_input)
    print(f"Valid number: {number}")
else:
    print("Please enter only digits")

✍️ Practice Exercises¶

Create a program that converts usernames to lowercase
Clean phone numbers by removing spaces and dashes
Validate email format (contains @ and .)
Count how many times a letter appears in a word
Create a function that capitalizes names properly
Build a simple text processor that removes extra spaces

📝 More Useful Methods¶

`.count(substring)`¶

text = "hello world"
print(text.count("l"))  # 3

`.startswith()` and `.endswith()`¶

filename = "document.pdf"
print(filename.endswith(".pdf"))  # True
print(filename.startswith("doc")) # True

`.strip()`, `.lstrip()`, `.rstrip()`¶

text = "   hello   "
print(text.strip())   # "hello" (both sides)
print(text.lstrip())  # "hello   " (left side)
print(text.rstrip())  # "   hello" (right side)

`.split()` and `.join()`¶

# Split string into list
sentence = "Python is awesome"
words = sentence.split()  # ['Python', 'is', 'awesome']

# Join list into string
joined = " ".join(words)  # "Python is awesome"
csv = ",".join(words)     # "Python,is,awesome"

🎮 Real-World Examples¶

Email Validator¶

email = input("Enter email: ")
if "@" in email and "." in email:
    domain = email.split("@")[1]
    print(f"Domain: {domain}")
else:
    print("Invalid email format")

Username Formatter¶

username = input("Username: ")
username = username.strip().lower().replace(" ", "_")
print(f"Formatted username: {username}")

Password Strength Checker¶

password = input("Enter password: ")
has_digit = any(c.isdigit() for c in password)
has_upper = any(c.isupper() for c in password)
has_lower = any(c.islower() for c in password)

if len(password) >= 8 and has_digit and has_upper and has_lower:
    print("Strong password!")
else:
    print("Weak password")

🚀 Challenge Projects¶

Text Analyzer: Count words, letters, vowels, consonants
Name Formatter: Handle various name formats (JOHN DOE, john doe, etc.)
Censorship Filter: Replace bad words with asterisks
Acronym Generator: Create acronyms from phrases (e.g., “For Your Information” → “FYI”)
Text Reverser: Reverse words and sentences in different ways

🎓 Key Takeaways from Video¶

Strings are text data enclosed in quotes
Define functions using the def keyword
Use if-elif-else for conditional logic

💡 These points cover the main concepts from the video tutorial to help reinforce your learning.

🔗 Next Chapter¶

Continue to Chapter 14: Indexing to learn how to access individual characters!