Regular Expression Code Snippet Generate

Here's a Python code snippet that uses a regular expression to validate an email address format: ```python import re def is_valid_email(email): # Define the regular expression for validating an email address email_regex = re.compile( r"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$" ) # Use the regex to check if the email matches the pattern return bool(email_regex.match(email)) # Example usage emails_to_test = [ "test@example.com", # Valid "user.name+tag+sorting@example.com", # Valid "user@sub.domain.com", # Valid "user@domain", # Invalid, no TLD "user@domain.c", # Invalid, TLD too short "user@domain.toolongtld", # Valid, unusual but technically valid TLD "@missingusername.com", # Invalid, missing username "missingatdomain.com", # Invalid, missing '@' "user@.domain.com", # Invalid, domain starts with a dot "user@domain..com" # Invalid, double dot in domain ] for email in emails_to_test: print(f"{email}: {is_valid_email(email)}") ``` ### Explanation of the Regular Expression - `^` and `$`: These are anchors that denote the start and end of the string. This ensures the entire string is validated as an email address. - `[a-zA-Z0-9._%+-]+`: This matches the username part of the email. It allows alphanumeric characters and some special characters (`.`, `_`, `%`, `+`, `-`). The `+` ensures that at least one character is present. - `@`: This is the literal `@` symbol, separating the username from the domain. - `[a-zA-Z0-9.-]+`: This matches the domain part of the email. It allows alphanumeric characters, dots (`.`), and hyphens (`-`). The `+` ensures that at least one character is present. - `\.`: This matches the literal dot (`.`) in the domain, separating the domain name from the TLD. - `[a-zA-Z]{2,}`: This matches the top-level domain (TLD). It ensures that the TLD is composed of at least two alphabetic characters (e.g., `.com`, `.org`). ### How the Code Works 1. **Compile the Regular Expression:** The `re.compile()` function is used to compile the regular expression pattern into a regex object for reuse. 2. **Match the Email:** The `match()` method checks if the input email matches the pattern from start to end. 3. **Return the Result:** The function returns `True` if the email is valid according to the regular expression and `False` otherwise. ### Example Output The code tests several email addresses, printing whether each one is valid: ```plaintext test@example.com: True user.name+tag+sorting@example.com: True user@sub.domain.com: True user@domain: False user@domain.c: False user@domain.toolongtld: True @missingusername.com: False missingatdomain.com: False user@.domain.com: False user@domain..com: False ``` This example illustrates how different email formats are validated using the regular expression.