<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def indentby(parser, token):
 """ Add indentation to text between the tags by the given indentation level. {% indentby <indent_level> [if <statement>] %} {% endindentby %} Arguments: indent_level - Number of spaces to indent text with. statement - Only apply indent_level if the boolean statement evalutates to True. """

    args = token.split_contents()
    largs = len(args)
    if largs not in (2, 4):
        raise template.TemplateSyntaxError("indentby tag requires 1 or 3 arguments")
    indent_level = args[1]
    if_statement = None
    if largs == 4:
        if_statement = args[3]
    nodelist = parser.parse(('endindentby', ))
    parser.delete_first_token()
    return IndentByNode(nodelist, indent_level, if_statement)