def convert(sum, length, *list):
    while length>=0:
            for x in list:
                new = int(x) * 16 ** length
                sum = sum + new
                length = length - 1
                return sum

sum = convert(sum=0, length=int(len(list))-1, *list)

sum = convert(sum=0, len(list)-1, *list)

sum = convert(sum=0, *list)

In [6]: def f(a,b):
   ...:     return a,b
   ...: 
 
In [7]: f(1,2)
Out[7]: (1, 2)
 
In [8]: f(a=1,2)
  File "<ipython-input-8-dda526ab872e>", line 1
    f(a=1,2)
         ^
SyntaxError: non-keyword arg after keyword arg
 
 
In [9]: f(1,b=2)
Out[9]: (1, 2)

sum = convert(0, int(len(list))-1, *list)