def digit_sum(z):
    list = []
    for i in str(z):
        list.append(i)
    print (list)
    for i in list:
        i = int(i)
        i += i
    print (i)
digit_sum(1234)

>>> def dsum(n):
...     return sum(map(int, str(n)))
... 
>>> dsum(1234)
10
>>>