array_index :
                       | NUM
                       | COLUMN
                       | COLUMN COLUMN

def p_array_index(self, p):
        '''array_index :
                       | NUM
                       | COLUMN
                       | COLUMN COLUMN'''
        if len(p) == 3:
            p[0] = slice(0, -1, -1)
        elif len(p) == 1 or p[1] == ':':
            p[0] = slice(0, -1, 1)
        else:
            p[0] = slice(0, int(p[1]), 1)