# if base is greater than 16, raise error

if base >16 or base <=0:

raise ValueError ('base must be between 1 and 16')

elif isinstance(decimal,int)==False:

raise ValueError('the number must be a integer')

elif decimal==0:

return str(0)

hex_num = "0123456789ABCDEF"

s = Stack()

while decimal > 0:

remainder = decimal % base

s.push(remainder)

decimal = decimal // base

output = ""

# want to pop all the stack contents out

while not s.isEmpty():

#hex_num[s.pop()] would make sure base>10, the alphabet would be used

output += hex_num[s.pop()]