How to Sanitize Filenames in Python

import re
from pathlib import Path

def sanitize_filename(filename: str, replacement: str = "_") -> str:
    """
    Remove illegal characters from a filename.
    
    Illegal characters: / \\ : * ? " < > |
    Also strips leading/trailing spaces and dots.
    """
    # Remove illegal characters
    sanitized = re.sub(r'[\\/:*?"<>|]', replacement, filename)
    
    # Strip leading/trailing whitespace and dots
    sanitized = sanitized.strip(" .")
    
    # Prevent empty filename
    if not sanitized:
        sanitized = "unnamed"
    
    return sanitized


if __name__ == "__main__":
    # Test cases
    test_filenames = [
        "my:file?.txt",
        "data/report*2022",
        "  photo (1).jpg  ",
        "invalid|name:<test>",
        "...",
        "normal-file.txt"
    ]
    
    for name in test_filenames:
        result = sanitize_filename(name)
        print(f"'{name}' -> '{result}'")