def isYes(string):
    """Returns True if the string represents a yes, False, if it represents
    no, and another string if it represents something else"""
    value = string.strip().lower()

    if value in ['yes', 'always', 'on', 'true']:
        return True
    if value in ['no', 'never', 'off', 'false', 'null']:
        return False
    if value in ['changed', 'change', 'onchange', 'on_change', 'diff']:
        return 'change'