When attempting the digit_sum exercise in practice makes perfect, I get the following error: Oops, try again. Does your digit_sum function take exactly one argument (a positive integer)? Your code threw a "'int' object has no attribute '**getitem**'" error.

Please see my code below (which appears to work in pycharm):

I do not understand why I get the error in codeacademy and not in pycharm. Is my code incorrect?

```
# Function to add components of a number e.g. 1234 = 10
def digit_sum(n):
list = []
list_tot = 0
for i in range (len(str(n))):
list.append(int(n[i]))
list_tot = list_tot + list[i]
return list_tot
numb_txt = raw_input('Enter a positive number: ')
print digit_sum(numb_txt)
```