import re


def _sanitize_label(label):
    """
    Clean up a label by removing non-letter, non-space characters and
    putting in all lowercase with underscores replacing spaces.

    Parameters:
        - label: The text you want to fix.

    Returns:
        The sanitized label.
    """
    return re.sub(r'[^\w\s]', '', label).lower().replace(' ', '_')