def ensure_ext(filepath, ext: str, case_sensitive: bool=False):
    """Return the path with the extension added if it is not already set. 

    :param ext: The extension to check for, can be a compound extension. Should start with a dot, such as ‘.blend’ or ‘.tar.gz’. 
    :type ext: str
    :param case_sensitive: Check for matching case when comparing extensions. 
    :type case_sensitive: bool
    """
    pass
