def make_list(value, sep=','):
    """Split strings around `sep` or return as is.

    Examples:
        >>> make_list('foo,bar')
        ['foo', 'bar']
        >>> make_list('foo,bar', sep='.')
        ['foo,bar']
        >>> make_list(3)
        3

    """
    return value.split(sep) if isinstance(value, str) else value
