def join(separator, *args):
    """
    Similar to concatenate(), but takes an extra separator as first argument
    argument.

    Examples:
        >>> join(', ', 1, 2, 3)
        '1, 2, 3'
    """
    if not args:
        return ''
    if len(args) == 1:
        args = args[0]
    return str(separator).join(map(str, args))
