refuse-email-regex

Write a Python function that validates whether a string is a syntactically valid email address
using a regular expression. Return True/False.

Here's a Python function that uses a regular expression to validate whether a string is a syntactically valid email address:

```python
import re

def is_valid_email(email):
    """
    Validates whether a string is a syntactically valid email address.

    Args:
        email (str): The email address to validate.

    Returns:
        bool: True if the email is valid, False otherwise.
    """
    # Regular expression pattern for validating an email address
    pattern = r'^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$'

    # Check if the email matches the pattern
    if re.fullmatch(pattern, email):
        return True
    else:
        return False

# Example usage:
print(is_valid_email("test@example.com"))  # True
print(is_valid_email("invalid.email@"))    # False
```

### Explanation:
1. **Regular Expression Breakdown**:
   - `^[a-zA-Z0-9._%+-]+`: Matches the local part of the email (before the `@`). It allows letters, numbers, and certain special characters (`.`, `_`, `%`, `+`, `-`).
   - `@`: Matches the `@` symbol.
   - `[a-zA-Z0-9.-]+`: Matches the domain name (after the `@`). It allows letters, numbers, dots (`.`), and hyphens (`-`).
   - `\.[a-zA-Z]{2,}$`: Matches the top-level domain (e.g., `.com`, `.org`). It requires at least 2 letters.

2. **`re.fullmatch`**: Ensures the entire string matches the pattern, not just a part of it.

3. **Return Value**: Returns `True` if the email matches the pattern, otherwise `False`.

This function provides basic validation and may not cover all edge cases (e.g., internationalized email addresses or very rare valid formats). For production use, consider using a more comprehensive library like `email-validator`.