Convert CamelCase to lower_and_underscore.

def decamelise(text):
    """Convert CamelCase to lower_and_underscore."""
    s = re.sub('(.)([A-Z][a-z]+)', r'\1_\2', text)
    return re.sub('([a-z0-9])([A-Z])', r'\1_\2', s).lower()