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🔍 Checking String Content

Python provides several methods to check and validate the content of strings. These methods are essential for data validation, input processing, and text analysis.

# Basic string content checking
text = "Python123"
print(f"Is alphanumeric: {text.isalnum()}")
print(f"Is alphabetic: {text.isalpha()}")
print(f"Is numeric: {text.isdigit()}")

🎯 String Validation Methods

Python offers a variety of methods to check string content and characteristics.

Basic Examples

# Different ways to check string content
texts = ["Python", "123", "Python123", "   ", "Hello World"]

for text in texts:
    print(f"\nChecking '{text}':")
    print(f"isalpha(): {text.isalpha()}")
    print(f"isdigit(): {text.isdigit()}")
    print(f"isalnum(): {text.isalnum()}")
    print(f"isspace(): {text.isspace()}")
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🔍 Pattern Matching

You can check if strings match specific patterns or contain certain content.

# Pattern matching examples
email = "user@example.com"
filename = "document.pdf"
text = "Hello World"

# Check if contains specific text
print(f"Contains 'World': {'World' in text}")
print(f"Contains '@': {'@' in email}")

# Check start and end
print(f"Starts with 'user': {email.startswith('user')}")
print(f"Ends with '.pdf': {filename.endswith('.pdf')}")

# Check case
print(f"Is lowercase: {text.islower()}")
print(f"Is uppercase: {text.isupper()}")
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🎨 Common Use Cases

Here are some practical examples of string content checking.

# 1. Validating user input
def validate_username(username):
    if not username.isalnum():
        return "Username must contain only letters and numbers"
    if not username[0].isalpha():
        return "Username must start with a letter"
    return "Valid username"

# 2. Checking file types
def is_valid_image(filename):
    return filename.lower().endswith(('.png', '.jpg', '.jpeg', '.gif'))

# 3. Validating email format
def is_valid_email(email):
    return '@' in email and '.' in email.split('@')[1]

# Test the functions
print(validate_username("user123"))
print(is_valid_image("photo.jpg"))
print(is_valid_email("user@example.com"))

📝 Quick Practice

Let's practice checking string content with a real-world scenario!

Hands-on Exercise

Create a function to validate a password.

python
# Password Validation Practice
def validate_password(password):
    # TODO: Implement password validation
    # 1. Check if password is at least 8 characters
    # 2. Check if it contains at least one uppercase letter
    # 3. Check if it contains at least one digit
    # 4. Check if it contains at least one special character
    
    # Return True if valid, False if invalid
    return False

# Test the function
test_passwords = ["abc123", "Password123", "Pass123!", "P@ssw0rd"]
for pwd in test_passwords:
    print(f"Password '{pwd}': {validate_password(pwd)}")

Solution and Explanation 💡

Click to see the solution
# Password Validation Solution
def validate_password(password):
    # Check length
    if len(password) < 8:
        return False
    
    # Check for uppercase
    if not any(c.isupper() for c in password):
        return False
    
    # Check for digit
    if not any(c.isdigit() for c in password):
        return False
    
    # Check for special character
    if password.isalnum():
        return False
    
    return True

# Test the function
test_passwords = ["abc123", "Password123", "Pass123!", "P@ssw0rd"]
for pwd in test_passwords:
    print(f"Password '{pwd}': {validate_password(pwd)}")

Key Learning Points:

  • 📌 Used len() to check length
  • 📌 Used any() with generator expressions
  • 📌 Used .isupper() and .isdigit() for character checks
  • 📌 Used .isalnum() to check for special characters
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🎯 Key Takeaways

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