For : FOR Expression IN Expression COLON Terminator Block
        | FOR Expression COMMA Expression IN Expression COLON Terminator Block

def p_For(p):
    '''
    For : FOR Expression IN Expression COLON Terminator Block
        | FOR Expression COMMA Expression IN Expression COLON Terminator Block
    '''
    if len(p) <= 8:
        p[0] = For(p[2], None, p[4], p[6], p[7])
    else:
        p[0] = For(p[2], p[4], p[6], p[8], p[9])