def force_list(obj):
    """Force object to be a list.

    If ``obj`` is a scalar value then a list with that value as
    sole element is returned, or
    if ``obj`` is a tuple then it is coerced into a list.

    """
    if isinstance(obj, tuple):
        return list(obj)
    elif not isinstance(obj, list):
        return [obj]
    return obj