def dectobase2(base, number):
        symb=["0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F"]
        global tb
        def tb(b, n, result=''):
                r = ''
                if n == 0: return result
                else:
                        while n > b:
                                r = symb[n%b] + result
                                n = n/b
                return tb(b, n/b, str(n%b) + result) + r
        if type(base) != type(1):
                raise TypeError, 'invalid base'
        if base <= 0:
                raise ValueError, 'invalid base : %s' %base
        if number == 0:
                return '0'
        if number > 0:
                return tb(base, number)
        if number < 0:
                return '-' + tb(base, -1 * number)
print dectobase2(16, 15)