I need to create a function that takes a list and a separator value as parameters and returns the string representation of the list which is separated by the separator value.

The only built-in functions I can use are `range()` and `str()` without any slice expressions, list methods or string methods.

I have put together some code but I know it isn't right as it is displaying a space at the beginning and the separator at the end (separator needs to be only between values).

How can I fix this? 

```
def my_string(my_list, sep=', '):
    string = " "

    for words in my_list:
        string += words + ', '     

    return string

my_list = ["item1", "item2", "item3", "item4"]
list_string = my_string(my_list, sep=', ')
print (list_string)

```