Newbie: last item of a loop

[your humble servant]

> my_names=['Peter', 'Paul','Mary']
> my_name_string=''
> 
> for i in my_names:
>   # if more than one name
>   if len(my_names) > 1:
>     # if not last or second-last name, append komma
>     if i.index  < len(my_names) - 1:
>       my_name_string = my_name_string + ', '
>     # if second-last append 'and'
>     if i.index  == len(my_names) - 1:
>       my_name_string = my_name_string + ' and '

Simply:
', '.join(yournames[:-1]) +' and '+ yournames[-1])