🔍 Finding & Replacing Text — Locate and Modify Content

Learn to search for substrings, find their positions, and replace them efficiently.

🎯 The find() Method

The `find()` method returns the index of the first occurrence. Returns `-1` if not found:

text = "Python is awesome. Python is fun."

position = text.find("Python")
print(position)  # 0 (first position)

position = text.find("is")
print(position)  # 7 (first "is")

position = text.find("xyz")
print(position)  # -1 (not found)

# Start search from specific position
position = text.find("Python", 10)  # Search from index 10
print(position)  # 20 (second Python)

💡 The index() Method

`index()` works like `find()` but raises an error if substring not found:

text = "Hello World"

print(text.index("o"))   # 4
print(text.index("xyz"))  # ValueError: substring not found

🎨 The count() Method

Count how many times a substring appears:

text = "apple apple apple"
count = text.count("apple")
print(count)  # 3

sentence = "The quick brown fox jumps over the lazy dog."
print(sentence.count("the"))  # 1 (case-sensitive)
print(sentence.count("the", 0, 20))  # Count within range

🔑 The replace() Method

Replace text with new content:

original = "I like cats. Cats are cute."

# Replace all occurrences
result = original.replace("cats", "dogs")
print(result)  # I like dogs. Cats are cute. (note: "Cats" not replaced)

# Case-sensitive replacement
result = original.replace("Cats", "Dogs")
print(result)  # I like cats. Dogs are cute.

# Replace first N occurrences
text = "one one one one"
result = text.replace("one", "two", 2)  # Replace first 2
print(result)  # two two one one

📊 Search & Replace Reference

💡 Real-World Example: Email Validation & Extraction

email = "john.doe@example.com"

# Check if it's an email
if "@" in email and "." in email:
    print("Valid format")

# Extract domain
at_pos = email.find("@")
domain = email[at_pos + 1:]
print(domain)  # example.com

# Replace domain
new_email = email.replace("@example.com", "@newcompany.com")
print(new_email)  # john.doe@newcompany.com

🎯 Conditional Replacement

text = "I have 5 apples and 3 apples"

# Replace only if found
if "apples" in text:
    text = text.replace("apples", "oranges")
    print(text)  # I have 5 oranges and 3 oranges

# Count before replacing
original = "The cat and the dog"
count_before = original.count("the")
result = original.replace("the", "a", 1)  # Replace first only
print(f"Found {count_before} occurrences")

🔑 Key Takeaways

🔗 What's Next?

Learn to validate strings and test characters.

Ready to practice? Challenges | Quiz