--- self[nth]=value

    ¤Τ nth ܤΥФͤ value ˤ 
    value ֤ޤnth ʸޤ Symbol ξ
    Ϥ̾ΥФͤ value ˤޤ

    ¸ߤʤФꤷ硢㳰 IndexError 뤤 
    NameError ȯޤ

